Best read for yourself, http://www.dmoz.org/about.html As far as the traffic question goes, the traffic that goes through the ODP is massive. However because it there are so many sites listed the amount that each individual site gets is not enough to get excited about. A significant aspect of the ODP is that an of information provider rather than a destination site. This is difficult to quantify in terms of the benefits to an individual site of the use of data by the third parties.