Despite how buzzword-prone their startup idea is, prediction markets are sexy right now for a reason. When implemented correctly, they can be quite informative -- or at the very least entertaining -- whether it's about who will be the Democratic Presidential nominee in '08 or who will win the Super Bowl. After all, none of us is as smart as all of us (despite what you may have read, I came up with this).
I've still be hurting from the $48,805.55 (in inkles, a fake currency -- thankfully) that I lost during last year's academy awards (thanks, Crash). Building and managing your own prediction market is cake if you're one of their corporate clients or Jane Internet-user -- although I've never tried as a corporate client... or as "Jane" for that matter, but it worked fine for me.
They've also just opened up worthio, which is much like a reddit for stocks, but clearly built by some folks who actually know something about the market.
And what their mascot lacks in detail (I believe they were going for the abstract-enough-so-anyone-can-relate look) it makes up for in quantity: +1 for lots of pretty-colored people-shapes.
YC Week is done for now, since the week is over, but it'll resume once we get into '07 and I inevitably run out of ideas again.