Crowdsourcing The Crystal Ball
forbes.com
forbes.com
An active market could be great with real money, though. I haven't heard any examples of someone making a huge amount of money by trading predictions, but if such a person emerges, the real-money markets would see a very nice spike in interest.
I wonder if these things are more or less susceptible than stock exchanges to people who profit by manipulating outcomes. If the number of people in a position to perform a manipulation is fairly small (and therefore relatively traceable), that danger is avoidable. The pool of potential manipulators gets pretty big, though, with certain types of predictions, like when a person will die. (In other words, someone could kill the target and make a lot of money. Let's call it the democratization of insider trading.)
And there are all sorts of markets that use real money to trade predictions. They're called futures markets.