At Overcoming Bias, Eliezer Yudkowsky invites pundits, partisans, and anyone else with a nascent opinion about the limits of prediction markets to, in effect, put up or shut up. (Though he puts it in somewhat nicer words). Here is a selection, but read the whole thing:

If you think that Hillary is going to do better than the polls on Super Tuesday, and you&#8217-re going to sneer afterward and say that Intrade was &#8220-just tracking the polls&#8221-, buy Hillary now.

If you think that Obama is going to do better than the polls on Super Tuesday, and you&#8217-re going to gloat about how prediction markets didn&#8217-t call this surprise in advance, buy Obama now.

&#8230-

The point is not that prediction markets are a good predictor but that they are the best predictor. &#8230- If prediction markets react to polls, they&#8217-re getting new information, that they didn&#8217-t predict in advance, which happens. Being the best predictor doesn&#8217-t make you omniscient.

Everyone&#8217-s going to find it real easy to make a better prediction afterward, but if you think you can call it in advance, there&#8217-s FREE MONEY GOING NOW.

Buy now, or forever hold your peace.