I had an extremely sudden battery drain while attending a function at the Hilton in Cambridge at the weekend. I started with the phone at 100% charge at 8pm. When I checked it 5 hours later it had drained to 2% (98% battery loss in 5 hours). I was able to take a quick look at BetterBatteryStats and the top two items on the partial wakelock list were the Nielsen mobile panel app and one of the Google NLP services, so I'm guessing that the phone was hunting for a data signal the whole time, and that was what was causing the battery drain.
Can anyone recommend an app that will disable data and/or wifi if no good signal is available, and perhaps re-check every 15 minutes? I remember reading about just such an app in the last couple of weeks, but can't remember what it was called and haven't had any luck googling it.