http://timharford.com/2013/12/of-bitcoins-bubbles-and-bq-vouchers/

Published in the FT a few days ago.
http://www.ft.com/cms/s/0/490585d8-5d07-11e3-81bd-00144feabdc0.html?siteedition=uk#axzz2mjHA3GpZ

Wilfully ignores the medium-of-exchange/unit-of-account distinction. Tim knows better than this.