I'm running OS5, my battery life isn't what it used to be that's for sure. I'm constantly checking to make sure I don't have programs running in the background that I'm not using. I also keep it charging in the car during long trips now just in case.
All in all I do like OS5, but my biggest beef is that with the additional space I have a lot less room for applications.
I wish I could put applications on the SD card, but you can't