I had to get a replacement black ops disc for my son when his xbox fell over and scratched it.. Cost £12 and took nearly 2 months for the replacement to arrive... with regards to the recipt, you only need it if its a warrenty claim within 90days.
You do not need it out off warrenty. 100% as i still have the recipt in the games manual. (you only send the CD for replacment, they actually send you a new boxed and sealed game)