Certainly don't let the big boys play with it. There's been some question floating around about how MF Global might have stolen their clients' money legally.
If I understand this correctly, while they're supposed to keep customer money segregated, they can offer part of it up as collateral for other bets. If the bets go bad, the client is out of luck and there's nothing they can do about it. So, uh, not so segregated after all.
License to steal. Or, more, specifically, a license to gamble with your money without your permission, and they keep the winnings while you eat the losses.
Fuck yeah!