In that analysis, I had web ads at about $38B by 2011.  Today I came across a report by Yankee Group on Paid Content that suggests I was being conservative:

— Online ad spend doubles in five years: According to the Yankee Group, the U.S. online ad market will hit $50.3 billion in revenue by 2011 - more than double 2007’s revenue. The underlying reasons for this rosy picture rests on the disparity between current media usage and spending by marketers. The web claims roughly 20 percent of overall media consumption in the U.S. right now - but advertisers currently invest only 7.5 percent of their budget online. The gap will start to be bridged by 2011, when Yankee predicts that online will comprise nearly 25 percent of all media consumption and 15 percent of the ad spend.

That is pretty impressive.  I had web ads taking in 25% as of 2020 and only 10.5% by 2011, but the more I think about it, that is too low cause in 2008 it will be about 8.9%…

Yankee sees the shift from offline to online accelerate much faster (which is welcome news to a web entrepreneur like me, mind you).