Lately my iPhone 4 has been sluggish and even crashed when opening certain Apps like the App Store or while Multitasking. The new location based reminders feature did not work on iOS 5 among other annoyances. What I did now was creating an iCloud Backup of my Phone, resetting it, and set it back up using the iCloud Backup instead of my local one. This seems to have resolved my issues, considering I´m carrying around my backup file since the day the iPhone 3G came out. I also did some jailbreaking in the past, so there was some bloat in there for sure. Must have been something in there that messed iOS 5 up. The point I want to make is that the Backup stored on Apples Server does not seem to have the same corrupted and messed up files stored as the Local Backup. This way it can be used to get the performance and stability of your phone back without losing data. Bet you could even do a fresh clean local backup now.