I'm one of the people that was caught by a previous owner's (or dealers fiddling) heating schedule.
However once fixed it is no longer a problem.
From my usage, the battery holds its charge very well when the car is just sitting unused, even after several days, the battery level hasn't decreased much, so if you manage to eliminate things like timers, there is definitely something to investigate going on.
My strangest experience with this stuff was driving to work on a cold morning... when I arrived, I had 10 km range showing on the guessometer, at the end of the day when I got in to the car, it was showing 18 km range!
My first thought was that someone had sneakily charged my car (as if!) but then realised that it was much warmer at 4pm than it was at 5am...