Battery life wasn't an issue honestly on iOS 4 (except for people in the 3G who upgraded to it, they appeared to have the most issue all around with iOS 4).
As far as bugs and stuff go...i think after the first real firmware update, many of the main issues were rectified, and the only big one that was left that never really found a true "answer" was the proximity sensor "bug".
Apple is very good about fixing problems, though honestly, i don't really see any major issues with this new 4S, the battery life issue might be something imbedded, but i honestly think people are using a much more powerful phone a lot more and its draining the battery like crazy (standing aside those who simply had bad handsets with batteries that were dramatically terrible).
If anything, they'll adjust power consumption and never tell us about it and we'll all just live happily ever after not really thinking about it anymore...battery is still a world better than my EVO, lmao.