Tag users

Google demands its adsense users to choose some trigger keywords/phrases. If they match a search of a Google user, the advertiser's ad might get displayed.

If the user clicks any such ad, they show interest in the topic of the ad, outlined by the trigger keywords. -- So, if one (or Google itself) were after to figure the interests of a user, Google could take these keywords and tag the user with them. -- The Google cookie one gets practically everywhere in the web, expiring in 2037, provides a unique handle for the user, for a long time. (And I really wouldn't wonder if they'd track 90% of all web users, individually.)

On the other hand, whenever a user enters a page featuring Google content, the user might become identified by their cookie. If Google is about to place ads on that site, by the cookie ID, Google immediately could figure the fields of interests of the visiting user. Also, immediately, it could update the user's record, since by visiting the page Google knew another bit about that user: He's likely interested in the topics dealt with on the page just entered. -- Which either the advertising real estate provider reveals by tagging its own page or which Google might do itself by traditional information science approaches.

Then, Google could select any ad that matches the user's profile and render it to the page currently being put out/the user is waiting for that it finishes rendering.
 

Is there a way to mimic that approach to gather tags of tags?

      
Updates: none so far