I don't remember exact usage scenarios or numbers, but when I put iOS 6 beta 3 on my iPhone 4S back in July, battery was incredible. A huge step-up from 5.1.1.
I think that after using the phone for 1.5 hours on iOS 5.1.1, I'd be at 80-85% battery and on iOS 6 I was at an incredible 90-95%. I wifi browse a ton so it seems like they have improved the battery in that regard. I could easily work a typical 9-5 work shift and still be at about 60% when I came home.
YMMV, of course. I could've just gotten lucky. 😀