It seems to come up quite a bit so I thought I'd measure it to see what it is. Luckily the heated seats have their own fuse which makes it easy to tap the circuit and measure the current.
The answer is about 3.25A per seat when the seat is heating. I sat in the car about 45 minutes playing around with the different H-M-L settings to see what was going on and here is what I saw:
Starting on Low I saw approx 3.25A for about 30 seconds then no draw (ok, 100mA or so) for about 1 minute, then repeat.
On Med I saw 1 minute at 3.25A and 40 seconds with no draw. On High I saw 3.25A constant and after 10 minute gave up watching for it to cycle. I got up and got out of the car and came back about 3 minutes later and it was pulling no current. About 15 seconds after I sat down it pulled 3.25A again.
This does not APPEAR to be a fixed cycle on any of these settings and here is why I say that. When I went from Med back down to Low it took over 5 minutes before it drew power again. This leads me to believe that the seat was warm enough that it didn't need to apply any current. Once it got into it's cycle it was again about 30 seconds on and 1 minute off.
So an approximation of average load per seat, which may well depend a bit on your ambient temp (mine was 50), using 13.8V for nominal voltage would be:
Low: 15 Watts
Med: 30 Watts
High: 45 Watts
Which means if my HV battery is a loaf of bread the heated seats are the crumbs in the bottom of the bag. I'm driving to work on High tommorow.
It just occured to me I measured with climate on Eco and there is a possibility, though it seems unlikely, that 'comfort' might yield different results. I'll check that and follow up perhaps this weekend when I have the time.