I am also seeing random BT disconnection issues. I am using an older style Apple BT keyboard, the one with the clear perspex bottom. At first I thought it was the batteries but even with a fresh set I see it disconnecting sometimes.
I have noticed it's mainly when I have left the machine for a little while. When I come back the no keyboard panel has popped up and I have to re sync the keyboard.
The keyboard in question has been in use for a good few years now, always worked 100% Only with the new MacPro (2.66 Quad) am I seeing this problem.
Not noticed an increase in battery usage though. If it carries on I'm going to ring Apple to see if there is a common problem.
Cheers
Cris.