I've owned both the Shidenkai and Ice, I haven't noticed my ice wearing and I've had it for almost 6 months? There are areas where my wrist sit, or center circle where my mouse usually moves, that has slight discoloration but no noticeable drag differences. It has so far lasted longer than my Shidenkai. The Shidenkai definitely reminded me of a coating that wore away, and the Ice feels more like a surface(you can't really tell its coated).
That being said, I've been busy moving the past few months so I haven't used it as much as I normally would have been. I love the Ice and would probably just eat the 35$ every 6-12months if it does wear out, just because I enjoy it so much.