Last week when my iPhone 4 failed an update from iOS 7.0.3 to 7.0.4, it was a disaster. The restore from backup failed, and it left about 10GB of invisible “Other” space taking up room on my phone. I had to wipe my phone again thoroughly to get my free space back.
The good news is iOS 7 is much faster on iPhone 4 after a factory reset, even with the exact same apps reinstalled! I’ve reached the conclusion that updating from iOS 6 to 7 can cause a massive slowdown for some.
If you think iOS 7 sucks and you’re having misc slowdowns such as slow rebooting, difficulty swiping to reach the camera, and keyboard lag, consider a factory reset via iTunes. It should do the trick.