Almost all of the time, if there's a bug, it's Your Fault™. But sometimes, it really is a bug in the API/OS. As iPhone OS is relatively new (especially 3.x) there are always a few bugs to look out for.
I think it would be a good idea to compile them in a list. If you know of any, please list them, along with which versions are affected, and if applicable any known workarounds.
It might save someone from pounding their head on their desk out of frustration when they're just experiencing an OS bug.