I've noticed that a lot of ES300's do not come with heated seats- so is this more of a rare option? Anyway, my question is that when I turn on the heated seats, they warm up quick, get really hot for several minutes then cool down. If I leave the button turned 'on', eventually they heat up again getting really warm for several minutes then cooling down. Is this normal?

 

For the heated seats in my '01 ES, they turn on and the heat stays on the entire time until I turn it off. I don't feel any sensation of the heat cooling off. For your case though, it sounds like you should have the heated seats checked out, particularly the heat elements underneath the driver (and passenger) seat.