Are you suffering the slow performance of your iPhone 3G with iOS 4 ??
If yes, here is good news for you ! Steve Jobs said they have fixed the most of problems in iPhone 3G running iOS4 in the iOS4.1 update.
I watched a video from winandmac.com and the performance seems improve a lot.
So be patience . iOS4.1 will be available in November .......according some news ...... ;-)