Forbes has an interesting story online about a legal online "sportsbook" (Centsports.com), where the owner gives "gamblers" 10 cents in their account, and if they bet it up to $20, they can cash out.

He makes money through advertisements, and since players never make deposits, it's not considered gambling.

Three elements have to be present to violate most state gambling laws--namely "prize, chance and consideration," says attorney Chuck Humphrey, a gaming-law specialist and author of the Gambling Law U.S. blog. Because Centsports.com doesn't allow users to bet their own stash, no "consideration" is involved, and thus all is kosher. Quips Palmer: "Congress assumes if you’re dumb enough to give away money, then go for it."
Full story here ... http://www.forbes.com/entrepreneurs/...egambling.html