My MDX's leather has 11x the mileage on it and 5 years on it and it might be in better shape than my G35s.

 

I can tell you that we just picked up my wife a 2008 Sedean Sport and compared to my 2004 coupe, her heated seats definatley suck!!!

 

I had an 04 G35 Sedan and an 04 350Z Roadster and they were equally sucky. I find they work 'OK' on really cold days but my heater core is generally warmed up before I feel the heated seat sensation. My car is still new and it's garaged parked so it does warm up quite fast, whereas the MDX has 82k miles and takes a little longer; however, its heated seats kick in long before the core gets warm. I can tolerate these heated seats and they're still A LOT better than no heated seats. I LOVE heated seats and use them all the time (mainly for my back muscles, etc.). The G35s work good enough in the cold, but suck royally when it's not cold. In fact, I think Infiniti has some sensor or something that won't even turn them on unless it's below 60F or something.