“Pay for Performance Gains on CPM” gives an excellent overview of this topic, which I feel is currently the hottest issue in online marketing.
I'd like to comment on the statement made by John Davis that, “[The big players in the space are] making a load of money on CPM deals. CPM deals are the most efficient way for vendors to make money.”
From my experience, this is inaccurate, as PlanetFeedback structures all of its online advertising on a pay-for-performance basis, including ads on several of the largest portals on the Web.
He is correct that sites would rather sell and almost always make more money on a CPM deal. However, Web sites have little choice but to compete with lower cost alternatives, especially when, in most cases, a majority of their inventory goes unsold.
• Rob Bunting