Here's another first hand experience. '05 X3 with 44K, and just recently it developed a hot spot on the driver seat, left side bolster. I smelled smoke and felt heat through my jeans and immediately turned off the seat heater - it was on max. The leather has a small burn mark on it, surrounded by leather distortion about the size of a quarter.
I called BMW NA at Woodcliff Lake, NJ and they said they had not heard of this problem and referred me to my dealer. They looked at it and said the heating pad was bad and would cost $800 to $1000 to fix, or $2000 for a new seat. Oh, did I mention the warranty is up?
Medium heat works okay for now, but I shift to low heat when the seat warms up.
Now to wait for a recall......