Not a whole bunch of volume yet.
Looks like it is modeled after Poindexter's scheme for predicting the likelihood of a future event occurring.
http://www.intrade.com/#
lol this site is sweet. I can trade bush's approval rating >:D
Here's another.
Iowa Electronic Markets ~ Current Markets
http://www.biz.uiowa.edu/iem/markets/
That's hilarious, Nostradamus would have a hayday if he were still alive. 8)