Its a coating on the watch and unlike the regular SS, you cannot buff out scuffs. I think from what I've seen and read its fairly durable but I suppose it really depends on how each owner treats/interacts with it.
I've had the SG, then went SS then went SBSS. While the SS is easier to remove light scratches like maflynn said, I have not experienced any problems with my SBSS and its been banged against A LOT of stuff. I find it much more durable then the SS to be honest.