Relative to dollars, nearly all commodities are hoarded, but that's because the entire money supply changes hands nearly 3 times a day on the currency markets (or at least used to). As bitcoin is backed by as much thin air as the other currencies, there is nothing to stop it's velocity from attaining the levels of the dollar.

Being as bitcoin is relatively new, its velocity is low; furthermore, as many vendors have not started accepting it, its velocity is further hampered.

The author suggests that it is mainly being used as a store of value, which is true. Any money that is not controlled by a government is generally a good store of value; and stores of value have their uses. Velocity is not everything.

It is worth noting, however, that throughout history "good money" (good stores of value) have always beaten "bad money" (bad stores of value) in the competition for velocity, all other factors being equal. The only place bitcoin has to catch up is in redeemability, otherwise it's suitability as a money is equal to the other fiat currencies. When it catches up there (and it will, since it obsoletes many taxes), expect it to really take off, unless governments start to get jealous and shove guns in everybody who tries to use it's faces.

Otherwise, most of his arguments are beaten by the infinite subdividability of digital currency.

I think what most of the critics of bitcoin don't realize is that soundness of a money is not dependent on it's backing or even how much is in circulation at any particular time. Who/what controls the issuance of the money is the most important factor; and the numerous hands on bitcoin assure things do not get out of hand.

My understanding is that it would be impossible to know. How could you tell the difference between a dollar that was being hoarded, a dollar that had simply not been spend yet, or a dollar that it's owner had lost access to? The way the system is set up, it is supposed to be impossible to tell even how much money a single individual possesses. One person could own half of all the bit coins in a massive market manipulation attempt right now, and I don't know how anyone could figure it out.