I've read anodized aluminum needs to be entirely resurfaced to get rid of any scratches. That's why I ordered a case for my MBP right away. Unfortunately I did get one little mark on the case before the case arrived but I doubt anybody will notice unless it's put under scrutiny.
Also your bottom plate has your serial number on it. If you take it into a store to be fixed and don't have the original, the discrepancy between the about box and the bottom plate may void any applicable warranty under the modification or defacement clauses.