That's a cool idea for getting people more involved. I have no idea whether its an issue, but I think we'll have to take a closer look to make sure we wouldn't run afoul of gambling laws.
(ianal, but) you probably won't. there are other sites out there that do exactly this, except i've not found one that isn't messy/spammy/etc.. would love to see something clean, flexible, and easy to use.