FWIW, I haven't experienced any notable degradation of the seats in my 08 (heated leather) with about 65k or either of my 09s (one heated leather and one cloth) with roughly 55k each. I'm a big guy, and my cars are split between Florida and it's inherent heat, and Michigan with the brutal cold winters.
My Michigan 09 developed a small indent from my wallet, but that's about it.
I'm really a small boned individual. The smart cars seats are comfortable for short trips around town. Never had a issues of the seat deforming, after 8 years of ownership. I've driven it many long distance drive. 3 hours is about all I can handle in the car. It seat cushion, are flat bottom. No real lumbar support. Or adjustment for it. The smart is a city car.