Don't know if this one has been posted (can't search right now), but I had an interesting crash that prevented my phone from turning on (would stay on the welcome screen 'forever').

Deleted the unsaved preferences and now the application switching lag is severely diminished (large db one still exists). I did lose my Hotsync ID, but I just synced with only one conduit active (iPhoto through Missing Sync) and clicked no when asked if I wanted to reinstall from backup. I also lost one registration key that I had to re-enter.

Phone is working again too...Crazy...