iLounge has highlighted this comment by one of their readers o n their homepage:
Originally a little miffed at Apple for not allowing Home screen wallpaper on the 3G but after a day of use, I’m beginning to think Apple should have added the iPhone 3G to the incompatible list alongside the original iPhone and iPod touch. This thing is painfully slow now. Were it not for the combined Inbox feature I’d have already attempted a downgrade back to 3.1.3.
Update: Several readers have shared via Twitter that their iPhone 3G handsets run just fine on iOS 4.