Charlene Li has a post entitled "The Slippery Slope of Search Semantics", in which she describes the various mental gyrations and contortions she's putting herself through trying to envision and size online marketing in 2010.

I'd be lying if I said I *knew* the answer (clearly), so instead, I'll point to a different path...

Aside from a minor gaff or two (at one point she refers to Contextual -- and Tacoda/RevSci -- when I believe she means Behavioral), the main issue I see with her analysis is that she's confusing the mechanism and format of search advertising. This is a Pit of Despair that I hope all of you will avoid (or better yet, take advantage of).

Charlene, if you read this, I'd love to talk more over coffee.