David Galbraith:

"Google have the expertise to develop a concept based approach, possibly using intellectual property gained through their acquisition of Outride, but they certainly need to get their act together here or text ads advertising Hummers from suvssuck.com aren’t going to be that impressive.
This is particularly important when you consider the following: "While clickthrough rates might indeed be lower, Google claims that their tests show that post-click behavior (conversions to sales) resulting from content-targeted ads is similar to that seen with search engine advertising.""

Exactly what I’m thinking about this whole content/keyword-based advertising. Look at your referrer stats. Lots of queries your blog is totally irrelevant to. Content advertising is an editorial choice (i.e. advertisers handpick publishers that seem relevant to their pitch and the audience they want to reach), and frankly speaking, Google algorithms are still quite "stupid" if you look at what they fetch for you.
04/23/04 update: Tim Bray: On Search: Intelligence.