Sounds like the iPhone OS 3.1 Update is Causing Crashes On iPhone 3G's so sayeth the Apple Blog. I've noticed mine has gotten a bit less stable, and my iTunes 9 has gotten really bad, as well as I've been hit by this bug, which seems restricted to only Canadian accounts.

Hopefully Apple will release a couple of updates to get things back to the stability of iPhone OS 3.0 and iTunes 8.x.