we ran a test over the holiday. both iPhone4 with latest iOS 5.0.1. synced same apps to both. power cycled both then fully charged. let them sit. one was at 99%, mine was at 78% after 8 hours of just sitting there; in the same room about 18" apart. all settings identical down to wallpaper (only difference is the phone number). both were purchased at the same time too; less then 6 months old.
i have to charge mine in the middle of the day now where prior to iOS 5.0.1 i didn't. the other phone behaves like it always did.