So that's an interesting topic. I have a couple apps that are crashprone, but honestly I almost never get crashes on my iPhone. All crashes get logged and put into iTunes. So its not just a "feeling". I have metrics.
One app I use that crashes often is USAToday. But looking at the last 30 days, I have seen only 4 apps crash, besides USAToday. And my usage is about 10 hours a day minimum.
The main reasons an app will crash often are shoddy programming frankly.
1) They don't handle low memory situations well.
2) They do multi-threading incorrectly (this is the most common one I've personally seen in my own code and in other people's - for example I just found a bug in PI where the status bar would sometimes not hide properly and I finally figured out after a lot of debugging that the call was happening in the sync thread and not the main thread as it should).
3) Poor memory alloc/release understanding.
On the iPad 2 you're going to see more of #2 because before having just one core multi-threaded bugs wouldn't show up as easily, but now having two cores simultaneously touching data, devs who wrote their threaded apps without thinking of atomic access and protecting data from multi-thread access will get crashes.
#3 I see constantly in the developer forums. So many developers have no clue how to do proper memory handling. The good ones don't have that problem though - much
This is the one place where I wish iOS had garbage collection like big brother Mac OS X.