Since I started writing applications for the iPhone, I learned quickly that some folks happily get their copy of an application not from the AppStore, but what can be called sites that crack iPhone applications. I did not look too much into it but from what I found it seems that there are some easy way to 'crack' an application on jailbroken iPhone. Apple should be addressing that problem rather than leaving the developer do their own anti-piracy code.
The good news is for us iPhone developers : it is easy to detect such cracked application and thus it's easy to disable a cracked application. The interesting part is that folks that crack applications stupidly don't really even try them after. For example Photo+Map has a built-in detection for detecting cracked application, and make the app unusable... But still the guy that cracked the application is too lazy to test what he just did and simply released the app to the various pirated catalog.
Without going into much details every single user that download the pirated copy is being tracked and I received on regular basis a report that could be used later to track the devices/users that usually pirate applications. In fact all my applications -even the Lite version- embed such anti-piracy measure. So if you are reading this post and are either a 'cracker' or someone that just installed one of my app and discover that it does not work, you know now that you just wasted your time.