I haven't seen Cowan's argument, but wouldn't the argument apply just as well to gold and silver, which were used for thousands of years as currencies?
Well, no. Concisely put, the problem is under-determined money demand because of readily available money or money-like substitutes (in the theoretical framework of money demand/money supply). This is an issue limited to the period of readily available new money, of which Bitcoin itself is one, really. For those thousands of years there were few such substitutes, and substitution would have been costly anyway, so the problem does not apply there.
There seems to be quite a bit of a Bitcoin interest around here, with several articles about it already: [1 2 3 4 5 6 7]
I propose that links and generic Bitcoin comments should be posted here, instead of making a new discussion thread for each interesting article about the subject.