It also might be interesting to see what fraction of users are selecting to have winnings routed to another address.
If the money goes back to the same address, it's hardly a very useful launderer.
Well, if I send my money to satoshidice with a public note saying "send my winnings back to 1MyOtherSecretAddress so they don't know it's me" then that's not a very useful laundry either.
I've seen this "SDICE launders money" argument before, but I think it's bogus. Everything they do is public, so is absolutely not laundering money.