There has been quite a few people with this same exact problem, when they turn the phone off it drains more then when it's on. (2.1 and 2.2 at least, not many complaints with 2.0) It's almost as if something is being left on and it drains the battery. I know it's not exactly #1 best idea, but you could try taking the battery out at night if that is the case. I know batteries will loose a small charge even if these is nothing that is using it, but never to the degree of which your talking about and it would take a few days to use up 5% of the battery. Another idea would be trying to put it in airplane mode before turning it off at night and seeing if there is any difference in the morning.