We’ve only had problems with new games. Specifically, games with double-layer DVDs. There aren’t many, Super Smash Brothers Brawl, Metroid Other M, and Metroid Prime trilogy are the only ones [del]my son[/del] I know of. The solution was to get a lens cleaner. (It may possibly have helped on Guitar Hero World Tour, which occasionally glitched briefly during songs.)
This probably isn’t your problem, since your lens shouldn’t get dirty that fast (unless you’re a heavy smoker), but if it’s one of those games, maybe a lens cleaner is worth a try.