I never thought I'd be joining this club. Also, I've come across a method of corrupting data that I didn't see mentioned yet in this thread.
I was in my blue Lancia Stratos. I wanted it stock again, so I put my card in Slot 2 then clicked Trade. I bought it from myself. Fine, nothing happened. But then, I sold the one I was just in. Afterwards, I got into the one I just bought from myself. When I clicked Get In, this notice popped up that said something like "The status of your garage (or car was it?) has changed. Are you sure you want to save?" I clicked OK, naturally. I wasn't sure though that it was a good idea to, and I almost didn't. But then I said "Whatever" and clicked OK. It began saving, then the game froze. I reset it, and when it would 'attempt' to auto-load my data, it once again froze. This only affected my main save and nothing else on my card, luckily.
But oh well, I'm much better at GT4 now than when I first started. I can start fresh in my quest to max out Bob's points, have a better win ratio (although I've actually destroyed it by trying to win high A-spec pt. races in the Sunday Cup, my first and only completed race.). I've done all the missions already, up to 23. And have 12 S-License tests to complete ("complete" = gold, for me). So I'm basically just looking at this as a way to get a good start, and to marvel at how easy this stuff is now that I've had enough experience in GT4 (I was 90% when my data was corrupted a few days ago).
edit: BTW, this might be a dumb question...but how do you link a club you're in into your sig? With words instead of the URL I mean.