Over the last two years, publishers have designated more and more of their inventory for the ad networks, with as much as 30% of inventory being pushed through them in 2007 (an increase from 5% in 2006) and likely much higher in 2008 (publishers like ESPN are the exception, as they no longer sell their inventory to networks). As more inventory goes into ad networks, buyers know they can push harder on prices, driving them downward.

An article on the growth of RSS advertising and the technical limits it presents for delivering interactive advertising. Good numbers on market penetration at the global level.

Has some interesting stats on UGC consumption across different target groups.