My S90D is just over a year old. Only minor creases as I would expect in a natural leather product, mostly on the side bolster that my rear end tends to hit as I slide and in out -- really not a lot different than I've experienced in my former Lexus, BMW and MBZ. Most of the actual wear is where the seat belt rubbed on the side bolster of my driver's seat, and on the piece at elbow-height that sticks out from the B-pillar -- from the first several weeks of ownership until I figured out what the issue was and began repositioning my seat getting in and out of my MS so those areas are not rubbed as much.
I am rather fanatical about wiping my seats (and dash) down with a clean and lightly damp rag every time I wash my MS (every week or two) to help hydrate the leather. I also clean off blue jean transfer and any dirt, especially from the side of the lower seat bolster and provide a general conditioning to the leather (Zaino or Leather Masters) every few weeks, just as I have with my former vehicles. In other words, I try to take care of the leather seats best I can and without a lot of hassle. The leather is after all a natural product just like our skin, so I've found a little simple maintenance helps keep my seats and other interior surfaces in better shape, compared to some other owners that may elect not to take that extra effort.
