Found this rather interesting study a guy at bored.com did. Kind of interesting, a few funny moments too.
http://www.bored.com/wallets/
Hey my wallet!! D:<...Those bass fu*beep*ers >:[
That's a lot more wallets that got returned than I would expect.
Expect nothing of the world, and it will always leave you pleasantly surprised.
I had my wallet mailed back to me, once. With $50 still intact!