This past spring, I purchased the expandable BMW side cases for my 650 gs. I was really suprised at how crappy they are! If you look at it too hard, you risk dents, dings, and scratches.
A friend owns the local Linex shop. You know, the spray on bed liner stuff for pick up trucks. It's really durable and suprisingly, light weight. I had him spray my bags and I think they came out great. Now it won't be so obvious if I have a little booboo.
(attempting to post a picture....let's see if it works)