The iPhone 3G with iOS 4 lasted 5 percent longer (10 minutes) than the iOS 3-configured iPhone 3G. Thatís not a big difference, but frankly, I thought battery life would decrease, not increase, after updating the OS. Interestingly, the iOS 3 iPhone took less time to download our rented movie than the iOS 4 iPhone 3G, though the application downloads were faster with the new OS.
Sidenote-my wife hates iOS4 on her 3G-slow, crashes, and slow, apparently...she ordered an iPhone 4 today-est. 3 weeks for delivery