Well I upgraded my iPhone 4 and iPad 2 to IOS 5.0. I immediately noticed a degradation in battery performance on both devices. My iPhone would not last a day with normal use, whereas previously it would last 2 days. My iPad would normally go from 100% down to about 80% when watching my video podcasts on the train. After the upgrade, it would go from 100% down to about 45% watching the same podcasts.
I did the usual "ask google" and this came up with a few common suggestions which I tried without much success. I then decided to just grin and bear it and wait for the inevitable fix from Apple. After a week or so, along came IOS 5.0.1 which supposedly fixed the problem.
I applied the upgrade and this has fixed the problem on the iPad. Battery life is back to pre-IOS5 performance.
For the iPhone however there didn't seem to be much, if any, improvement. I was showing my wife the differences between IOS 5 and IOS 4 when she asked me "whats that funny little arrow thingy?". I hadn't noticed before but location services seemed to be constantly on and this was what seemed to be draining the battery on the iPhone.
I don't allow many apps to utilize location services unless it seems appropriate (e.g. maps, foursquare etc). I went into the settings and turned these off one at a time until I found the culprit. It was FourSquare. Whether a change in IOS5 or an existing bug caused this, I don't know. What I do know though is that turning off location services for FourSquare made the "funny little arrow thingy" go away and when I then turned location services back on, it only appeared again when I was actually doing a location search in FourSquare.
My iPhone is now back to pre-IOS5 battery life. I can only suggest that if you are having battery problems under IOS5, investigate your location settings.