I think I have a similar problem like Ricky21 is having. When I drive home, my seat gets really hot, even hotter than what the hot setting is at. At one point, it gets unbearable sitting in it. The next morning, my battery was dead.
I then replaced the switch to see if that would fixed it with another used switch. That worked for a few weeks, and then it started doing it again, coming back from work. I unplugged the switch, and let the car sit for an hour. When I went to check on it, the seat was still hot, and it seemed it was still heating the seat, even though the car was off. I then pulled the fuse, for the HSEAT/LUM(I think that's what it was called). Then I checked on it 15 minutes later, and the seat was cold.
This person seems to have the same problem I'm having, so I'm assuming that's the problem with my car, with the control module for the heated seat. Unless I'm unlucky with having two switches fail withing a few weeks, which is possible with a used switch.
I've had this problem since November, and haven't gotten around to replace the control module yet, to see if that is the actual cause of it.