In other fields, it's not so clear. In a critique of Benkler's work last summer, business writer Nicholas Carr speculated that Web 2.0 media sites like Digg, Flickr and YouTube are able to rely on volunteer contributions simply because a market has yet to emerge to price this "new kind of labor." He and Benkler then entered into what has come to be widely known in Web circles as the "Carr-Benkler wager": a bet on whether, by 2011, such sites will be driven primarily by volunteers or by professionals.