All bets * (1-.981). That is roughly how much the house is expected to rake.
Think of SatoshiDice as a laundrer, it returns you 98% (roughly) of your money over time. Now some people play wierdly trying to "beat the numbers" and they might actually lose 100% of their money. That sweetens Satoshi's profits. But as Dooglus has shown, pretty much it's just laundering and taking a 1.9% fee.
Thanks for the stats folks
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.