As usual, one of us econ geek bloggers asks a question, and then the other econ geek bloggers have to respond in ways that show how smart we are. I hope I am not misrepresenting him, but Bryan Caplan is basically saying, "Austrians claim you can't model the future with probability distributions. But I am still waiting for an Austrian to model the future with probability distributions to clarify their claim."
Tyler Cowen and Arnold Kling have the right instinct--namely, Caplan is being goofy--but they get into all sorts of sophisticated examples and analyses. No, the Kirznerian point is quite basic; you don't need to look at derivatives markets to see its implications.
(My own, less wise-alecky answer is in the comments on Bryan's original post. HT2 Pepe for originally alerting me to this debate.)