I got my 4S on Friday and restored it from my 4 on Friday evening. Put it on charge overnight as usual and took it off charge around 7:30am on Saturday. As usual on a weekend, I didn't use it much. My 4 would usually end the day (around 11pm) with 70% battery left on a weekend. Weekday it would be around 50%. My 4S turned itself off at 9:30pm because it had run out of battery!
Charged it up again on Saturday night and the on Sunday it lasted a little better even though it still wasn't used much. Finished at 11pm with about 11% left although it had been topped up a little earlier.
It's been pretty much the same every day this week - nowhere near as good as the 4 and I've not been using it any more than my 4. If anything I've been using it less for fear of running out of battery when I need it!
Last night I did a restore through iTunes and set everything up as new - didn't use the backup. Same problem this morning with the battery running down very quickly (currently 92% and it's been off charge for 2hr 20mins).
One thing I've noticed is that the Usage figures (Settings->General->Usage) don't seem right. I've been noticing the "Usage" figure going up even though the phone has been locked. I know it goes up when it does certain background tasks, but yesterday it said "Standby 12hr 1min, Usage 9hr, 29min". There's no way I've used it for 9 hours yesterday.
This morning I've been turning things off one by one - bluetooth, push, siri, notifications, location, email, wifi, until finally putting it in airplane mode. No matter what, the usage still keeps going up (eg lock the phone, then unlock it a little while later and the standby has increased by 9 mins (correct) but the usage has increased by 7 mins). The only thing that stopped this usage increasing was when I put it into airplane mode.
I've also made sure I killed all the processes in the multitasking bar, reset network settings, reset the phone, restarted the phone, turned off location services....
My old 4 never did this and my wife's 4 only increases the usage when she is using it. The battery life I used to get on my 4 was excellent all the way through every beta of iOS 5 and when the final release was put on.
I'm in a really good signal area and I've not been moving around.
It looks to me like there is some rogue process running in the background and using too much power which only seems to affect the 4S. I've made an appointment with the Genius bar so hopefully it's just a dodgy hardware and it will be replaced and all will be good again. I guess it might be something in the iOS though and that will be sorted (hopefully!) in a point release very soon....