I was having exactly same problem for the last week or two until yesterday (except my unexplained high CPU usage was massively affecting performance). I couldn't figure it out and was ready to reflash it until I decided to try running the 1.1.1 update it has shown available for the last couple of days (I'm in the UK) in case this helped. Suprisingly this seems to have sorted the problem completely and myh CPU usage is down and my battery life back up. Obviously this doesn't help root out the cause of the problem but as long as it doesn't go back to the way it was I'm not too fussed.