A few comments and finding from me so far:
In a sense I have been in a position where it has been easy for me to try to track down the issue as ever since ios5 on my iphone 4 my usage time has equalled my standby time (In Genreal, Usage, at the bottom). Thus the battery would drain within 5 hours say (totally). So i knew the phone was constantly active doing something. So turning things off and checking the difference between usage and idle time would show me what it was that was running.
Yesterday I turned off iMessage and for about an hour that did the trick. Standby time ticked along while usage remained stationary. Horray, issue found! Well, no as when I got home about an hour later the usage started to move along again at a 1 for 1 rate with standby.
Then I read the above re removing email accounts and again for a while that seemed to do the trick. I had 25% battery left when going to bed but unfortunately my phone was off and dead this morning when i woke up and an inspection of the usage time again shows that it spent most of its time being 'used' whilst on standby over night.
So for me so far it seems some of the suggestions here solve the issue they seem to only temporarily solve the issue. I'm just fully charging it again now and will do some more testing today. But it seems to be a process that my phone gets in to doing constantly in the back ground. I guess that could be related to my icloud account where it gets stuck in a loop sync'ing something (mail / contacts etc) and that might be account related (on the server) which is why this is not an issue everyone has. But so far I think its a fix Apple need to come up with. But I'll keep searching and trying.
Before my battery would last the day but now its dead by around 2pm. I have a screen shot of my battery on 2% with Usage at about 4.5 hours and Standby or 4.5 hours. ie I tookit off charge and for the following 4.5 hours it constantly did something even though 4 of them it would have been in standby mode, and then died 4.5 hours later! I think some people are on here saying my battery is worse and are relating to differences of 10-20% and that turning x,y and z off helps this but there is a bigger issue going on here for some of phones dying in 5 hours.