Ok, yesterday I started taking usage screenshots of my ( AT&T ) iPhone 4 on iOS5. I got my friend to start doing the same on his iPhone 4S, and we are going to track our usages until 5.0.1 is released. Gonna put my money where my mouth is =P
personally, i can definitely tell a difference. not necessarily statistical, but where i have ended up at certain points of my day with typical usage. standby time is great too