Things like this are why I support "piracy," as it were. I don't pirate games per se, but I damn well make a backup of ANYTHING before I loan it to anyone. For the kids, I always try to find a way to harddrive it (Xbox/PS2). Really, really looking forward to that shitty looking dash update in the fall for the 360, if for no other reason than I will now be able to put a $60 game on the harddrive and not have to worry about a game getting ruined.
Like others though, tragedy strikes: when I was younger, the 5 year old loved to BITE ON THE GAMES. I still have a few of the discs with her bite marks in them. I guess I'm just too lazy to replace them. Heh.
Have any of you seen those professional grade resurfacers? The ones that do two discs at a time (GameCrazy/FYE/etc now sport them). When I worked at GameCrazy, we were the first ones in the state to get our hands on one, and I had a tough time explaining to more than one customer that we ruined their GameCube disc when we resurfaced it (we were still learning, and the Cube discs have that stupid ring of data..). That's worse than just wrecking it; having to tell someone you wrecked it and can't fnid another copy to replace it is infinitely worse. Yike.