http://ajnaware.wordpress.com/2010/01/08/five-good-reasons-not-to-implement-in-app-purchase/

Reason 1 – It is not trivial to implement it well

There is plenty of sample code available that you can use to implement the in-app purchase process, but you still need to design and implement your own “storefront” which displays information about the purchase, how much it costs etc. You also need to make sure your app logic works correctly both with and without the purchased items having been activated, and although this might be straightforward in apps where the content is already well compartmentalized, it is much trickier in other types of app where different app features typically have some integration, and need to be separated out carefully when split into standard/purchased functionality.

Testing that the purchase process works correctly and that the purchased content is made available correctly, and if necessary also registers on your own server, is also much slower and more difficult than ordinary app debugging, as it requires using a test sandbox accounts and server interactions. You also ought to test what happens if the purchase process is interrupted, or the server connection is interrupted during purchase or after purchase confirmation, but before you have saved the app purchase status to your own server. All these things can and will happen sooner or later if you have any significant number of users, and you will want to make sure you can deal with them all, and at least recover gracefully later if they can’t be dealt with up-front.

Reason 2 – The developer must take full responsibility for correct delivery of the purchased item

With a normal app purchase the developer can wash their hands of the sale process. Apple deals with the entire sale process and installation of your app, and if something goes wrong with that, and a user loses or needs to restore their purchase, install it on a separate device, or has any other issue, then it is Apple’s responsibility, and you are within your rights to refer any complaints about this back to Apple.

However, with an in-app purchase you suddenly take on much more responsibility. Although Apple does keep track of in-app purchases itself, and can restore these to the user, you will probably also want to keep track of purchases too – at the very least a database of app ids which have made the purchase, so that if the user simply re-installs their app, the app can determine on startup whether the purchase was already made previously, so they won’t have to go through the in-app purchase process again to get it back. Of course if you want to offer a trial, as I did, then you will have to maintain a similar database to keep track of that too.

The most difficult scenario, though, is if your in-app purchase is a time-limited subscription. In that case, Apple has no record of whether or not the subscription has expired, and it is totally up to you to maintain correct reliable records which can be used to restore each users app state. If anything goes wrong with your implementation of this, then it is you who will be responsible for refunding your users! Will you be able to sleep at night knowing this?

Reason 3 – A lot more user support and interaction is required

Although most users will already be familiar with app purchasing paradigms, many users have not used in-app purchase before, and this means that you will likely get a lot of queries due to their inexperience with the process and its quirks and implications.

Here is a list of some of the types of new user issues I’ve had to deal with as a direct result of the in-app purchase, for example:

• Questions about why they get a message saying purchases are disabled on their device
• Questions about why they get a message about a “Test User” account when they try to purchase (jailbroken devices)
• Questions about why they get a message about “Sandbox Account” when they try to purchase (jailbroken devices)
• Questions about why the in-app purchase apparently did not register on their device
• Questions about how to restore the purchase if they load the app onto a different device
• Questions about why they are told they have to purchase the original app before they can buy the in-app item
• Questions about why the in-app purchase items are not free to them, given that they already paid for the app

And then there were more issues relating to the trial, rather than to the purchase per-se, for example:

• Questions about exactly what the new features contain, after their trial has finished
• Questions/complaints about why they have lost trial features they believed were part of the standard app

Reason 4 – Users who don’t/won’t pay for the in-app purchase can still leave a bad review about it

In my own case, this is the hardest one to deal with – and should give other developers plenty of pause for thought.

Apple has gone to some lengths to tidy up the user review system, and it has certainly improved a lot since the early days. However, there remains a glaring hole in the system – although users can no longer leave reviews for apps that they haven’t purchased they can still leave reviews relating to in-app purchase items that they have not (and obviously will not) purchase.

In my own case, most of the bad reviews are apparently due to misunderstandings by the user about the nature of the in-app purchase. Some people obviously thought that they were losing what they had previously paid for, and had to pay again just to keep the app.

Of course I have to take responsibility for any lack of clarity in how the in-app purchase has been presented to the user, and I have indeed attempted to tweak this. I suspect that the worst reactions have come from people who for one reason or another, did not see the message that appears at the start of trial, explaining what was happening, after which they assumed that the trail features were theirs to keep. I’ll continue to work on this, and this might help, but the basic issue will remain as a major potential problem for anyone implementing in-app purchases, and wants to maintain a strong app rating in the store.

Reason 5 – Some users have the impression that all app “upgrades” must be free

Quite apart from users who misunderstood the trial and in-app purchase structure, there are also a number who simply seem to feel entitled to any additions to the app for free, perhaps having misconstrued Apple’s free update system as meaning that all types of app updates in functionality must necessarily also be free.

In a way it a compliment of course – the fact that they are so upset about not having the extra functionality must mean that they really do want and value it. However, the fact remains that these people also leave bad reviews, and there is no shortage of others who find those bad reviews “useful” and vote accordingly, thus pushing them to the top of the review list.

Ever wish you can count down birthdays, anniversaries, holidays and appointments all in one place? Here’s your chance. Big Day Countdown makes it simple to never forget a special event in your life.

Are you bored with other countdown or event tracking apps which have only simple text, small image? Big Day Countdown give you a totally different and unique experience with full graphics effects!

Download from here: http://itunes.apple.com/us/app/big-day-countdown/id371089933?mt=8

WHAT MAKES BIG DAY COUNTDOWN SO SPECIAL?

-Big Day Countdown is a FREE application built with sophisticated technology;

-You can import all your friends’ birthdays from Facebook and from iPhone contacts in 1 minute;

-Gracefully displays the days remaining until special events or birthdays (with age and photo!)

-You can make your own greeting card with finger and send it to your friends in one minute!

-The greeting card for every countdown event is fully customizable: Background, Font, Color and Layout;

WHY FREE BIG DAY COUNTDOWN BEATS PAID APPS OF THE SAME KIND?

-Large data support: you can create and store as many events/days as possible! No performance loss!

-Full-featured event/day management: adding, removing, editing, searching, importing, publishing

-eCard maker: high-quality background images, 10+ different fonts, 10+ text colors, zoom/shrink/move text by gestures

EXAMPLE USES:

-remember a friend’s Birthday and family Birthdays

-send a greeting/happy birthday to your wife, children or best friends

-see how long until Christmas, New Year, Halloween, Thanksgiving, etc.

-count down your Parties, Concerts, Festivals, Vacation

-keep track of your plans,  goals, due jobs

-view upcoming business events like scheduled interviews or meetings

TIPS:

Each update will deliver new drawings (backgrounds, fonts, color and even emotions!)

You can use In-App Purchase to remove the advert banner or just keep using the application for FREE.

Push Notification will be available within 2 next updates.

Ever wish you had all birthdays in one place? Here’s your chance. Birthday Calendar will help you track all those special days in your life.

With this free app you’ll never forget any birthdays by:

- View upcoming birthdays with age, zodiac, photo and countdown in a calendar format;

- Import birthdays from iPhone contacts & Facebook by one-click;

- Publish birthday countdown to Facebook or send it by mail;

No need for more description. Intuitive UI and operations make it so handy. Why not have a try?

Available at iTunes Store: http://itunes.apple.com/us/app/ibirthdaycalendar/id367346406?mt=8

Screenshots and User Manuals:
1. In default view, you will see your friends’ photo, name, birthday, age, zodiac and category (from Facebook, from iPhone contacts, or created by iBirthdayCalendar). You can also see the countdown to next birthday in rightmost column:

2. By switching to calendar view, you can see all above information categorized into different date sections:

3. You can add a new birthday by clicking “+” in toolbar. You can pick up a friend from iPhone contact, and if you choose “Update birthday to contacts”, the new birthday will also be recorded into this contact in your iPhone address book. If you don’t know exact year when your friend was born, switch off “Known Birth Year”:

4.  You can import friends from Facebook or iPhone contacts. Important: re-importing will replace all your existing imported birthdays in this category (facebook or contacts) with new imported ones.

5. You can view details for each birthday, you can edit the birthday in this page and publish birthday countdown to Facebook or email:

6. Edit/Delete a birthday:

Currently you cannot rename a contact but you can delete it then add it again.

To delete a contact, just follow default iPhone table row delete scheme:

Delete button: Users tap this element to delete the list item. This element appears to the right of a list item when users swipe in the row or when they tap the delete control button while in an editing context. 
From:http://developer.apple.com/iphone/library/documentation/UserExperience/Conceptual/MobileHIG/ContentViews/ContentViews.html

Also a “Delete this contact” button is in “Info” view, this will be more intuitive.