My DROID avg's 18 hours till charge time (30%).
I use the net alot during the day music phone....well lets just say some of everything.I am very satisfied with the battery performance.
Now that said ,I have had a few times that my DROID would get warm in my shirt pocket.Warm enough to draw my attention and when I would check it the batt is showing a large drop and the GPS is flashing active.Turning off the GPS will stop it,or a reboot will fix it and allow me to leave GPS on.
As what causes it hmmmm it has to be the browser,I had read here that if you exit the browser with the back button the GPS might not go off and that you should exit with the home key.Ever since I started exiting to home my GPS has not stayed on since.