RealClimate.org, the premier global warming blog, has a post on betting. I really like this comment:
"The auction market does not depend upon classical efficient market theory as much as it depends upon people's natural caution -- the fact that losing hurts more than winning gives pleasure. This tends to tone down "wild" claims that normally take precedence either in a group of similarly-minded people or in the race to be noticed by the media."
I think that's an important reason why betting is valuable in affecting the debate - in other words, "put up or shut up."
Science policy blog Prometheus has a post. I think he misses the point about the value it has in affecting public dialogue, however.
And at sci.environment, we may actually have a bet agreement, although it's only for $25 and the denialist hasn't acknowledged that his bet offer has been accepted.