My disc is fine, and always has been *knocks on wood*. But that's because I'm careful over my games and DVDs. You need to take very good care of your discs (games), as a little scratch, made from simply dragging it a little while picking it off a table, can cause a brutal glitch. Its not like a cd, where you'll just hear a skip in the song, and it'll go on. A scratch causing a glitch in the game could make it freeze, making it impossible to pass a certain point.

But yeah, try cleaning it, using a proper disc cleaner. You might be able to bring it somewhere, and have the disc re-furbished if cleaning it doesn't work.