The only other thing you may notice with resurfaced discs is a whitish 'film' on the bottom side of the disc. That is usually just some leftover residue from the resurfacing machine, which usually doesn't do anything to the games themselves.
I've noticed it on all of my games I've had resurfaced.
My one local game store, which sells games pretty cheap in most cases anyway, has a couple resurfacing machines. The owner just got in a pro model one about 6 months ago after having one of the desktop models like I've seen in GC stores.
He must make a mint off that thing each week, since every time I go in there, he has stacks of cd/dvd based games to resurface that are literally 3-4 feet high stacked next to each other and sometimes the stacks are 2 and 3 deep.
He used to do it for free, but then started charging the same as GC,$2 per disc, which still isn't too bad considering.
I just wonder though, is it legit if you took in a harder to find game to be resurfaced and then listed it as MINT in an auction or ad afterwards?