Many of Caplan's complaints are about Hayek's poor writing, and regarding his ideas Caplan has focused more on "scientism" than "the knowledge problem". A much more relevant Caplan post on that (probably aimed more at Mises, but applies to Hayek as well) is The Socialist Calculation Debate: Me Against the World

I don't care for Austrian economics and don't bother to read Hayek in the original, but I think the insight discussed here has been useful. Lin Ostrom, James Scott and William Easterly have all gotten a lot of mileage out of it, and while I don't think she cited Hayek (haven't finished the book yet) Jane Jacobs did as well from a less academic perspective.

I don't think Hayek believed any regulation leads to totalitarianism. On the contrary, I think he actually endorsed a number of them.

For someone who thinks this problem does severely cut against Wal-Mart, see Kevin Carson.