After upgrading to iOS 5, my iPhone 4 ran hot, was unstable (apps, including texts/iMessage would crash often) and the battery life dropped off tremendously, losing 10-20% per hour while in "standby"! I did some research and found that many were experiencing similar issues with iOS 5. I tried all recommended battery saving techniques, including turning off features (location services, notifications, push email, etc) as well as hard resets, removing all data, reseting network settings, deleting email accounts, and restoring the iPhone (from backup). Nothing helped! I really did not want to try the "nuclear option" - restoring & setting up "as a new phone", which many recommended. As a last ditch effort, I tried resetting all settings (Setting > General > Reset > Reset All Settings) and this fixed the problem! The battery is back to losing ~1% per hour while on standby, even with location services and all other battery draining features turned on. If you're experiencing horrible battery drain on iOS 5, I encourage you to reset all settings and let me know if this works for you as well.