I've been using it since the weekend, and battery life is superb - at least 50% better than ICS. The phone has been going fir 11hrs today, moderate use of Facebook, Twitter, internet, text, emails and a few phone calls and my battery is at 47% now. It *easily* lasts a full day now. I'm using full power save mode mind.
No issues with the upgrade - it downloaded and installed, and my phone was exactly as before as far as apps and data were concerned. No trouble at all.
I love the phone even more now!
Sent from my HTC One X using Android Central Forums