If you are an iPhone user and if you luckily hadn't updated its OS to 2.0.2, don't do it and wait until the next update.
I am one of the users who is experiencing the App Crash bug.
Some say that they were able to fix the problem by installing a new app from App Store; it didn't work for me.
My friend, Matthew Skyrm told me he got to fix this problem by authorizing the computer using iTunes and sync'ing, but it didn't work for me.
The only thing that worked for me so far is to "restore" the iPhone.
But even after restoring, if you buy a new App from the App Store, it could re-initiate the problem.
Restoring is a painful process especially if you find out that your backup file is corrupted and realize that you have lost all the data (from your MotionX score to Recorder's recordings and photos and SMS and notes, of course) and that you have to start over with all the settings, etc. etc.
If you already have upgraded to 2.0.2, be careful and don't buy too many apps from App Store until the next OS update.
OS 2.0.2 seem to be working fine for a while but it seem to break some DRM info while installing/updating your apps (via App Store on your iPhone).
The second time, I got into this problem was after I purchased an app from App Store; the app didn't finish installing for a LONG WHILE. And I had to power off the iPhone while the app didn't finish installing.
After the reboot all third party apps stopped launching.
Apple Insider says SJ is promising a September update to fix this, but I think this is more serious than he thinks.
I can't say for sure if OS 2.0.1 didn't have this problem (but at least to me, it didn't).
I hope Apple will re-release OS 2.0.1 as an OS 2.0.3 update very soon.
iPhone will be launching iPhone in 20+ country today possibly with the OS 2.0.2; I hope it doesn'T evolve into a serious problem.