I have an 07 GS350 with the same issue. I don't feel the driver's seat cooling at all but my Lexus dealer just checked it last week and advised me that both front seats are operating normal. There are a bunch of other disapointing features in this car that work "nomal" per Keyes Lexus in Van Nuys, Ca.
Overall I feel a Lexus is a great looking piece of crap.