This looks like a good place to post what I think is the best critique of the Austrians out there: Bryan Caplan (who is sympathetic to the Austrians) does a good job of arguing that the Austrian foundations fall into two categories 1) not different than mainstream economists 2) wrong.

It starts here Why I am not an Austrian economist, continues some back and forth between Walter Block and Hülsmann (an Austrian) and Caplan:

• Caplan, Bryan. 1999. "The Austrian Search for Realistic Foundations,"
• Block, Walter. 1999. "Austrian Theorizing, Recalling the Foundations: Reply to Caplan,"
• Caplan, Bryan, 2000. "Probability, Common Sense, and Realism: A Reply to Hülsmann and Block,"
• Block, Walter. 2003. "Realism: Austrian vs. Neoclassical Economics, Reply to Caplan,"
• Caplan, Bryan. 2003. "Probability and the Synthetic A Priori: A Reply to Block."
• Block, Walter. 2005. "Rejoinder to Caplan on Bayesian Economics,"
• Block, Walter. 2007. "Reply to Caplan on Austrian Economic Methodology"

There's more here (links from the appendix 1). Some of these are in .doc form.

I should also point out that I do think the Austrians are more correct than mainstream economists on several issues, but I don't think these follow from their epistemology.

I will also add that this discussion highlights that LWers should be particularly good at seeing the epistemic flaws of the Austrians since they are 1) a rejection of the use of probability theory as a fundamental part of decision theory 2) a rejection of utility functions 3) abuses of language (they frequently attempt to argue "by definition").