Learned about this from <snip> (no affiliation except as a reader of that blog).
Some of my thoughts:
It's interesting, but perhaps not surprising, that Google is first focusing on letting the ad viewer determine relevancy, instead of making this a publisher control panel option of sorts.
I wonder to what degree site visitor choices will affect ongoing relevancy determinations; e.g., if a lot of visitors click on "fruit baskets" on a page about the Apple software company Delicious Monster, will Google start showing fruit basket ads by default?
Along similar lines, could competitors / jerks decide to use this to negatively affect others' AdSense campaigns (e.g., repeatedly searching on or clicking on focus links that change the focus of the ad block to something really irrelevant)?
Will this new feature dramatically increase publishers' AdSense income? (I doubt it'd cause a decrease in income... or am I missing something here?)
[edited by: Jenstar at 9:11 pm (utc) on Jan. 25, 2005]
[edit reason] Sorry, no links to non-authority sites [/edit]