What would make things /really/ fast is optimizing an ad based around what brought a person to the page, rather than anything in particular about that person.
In other words, use referers to figure out if they came in based on keywords from a search engine (ads targeted more towards that, but still biased to the page viewed) or otherwise just based on the content of the page.
That's it; the first can be quickly memoised across a set of common terms for a page (and while doing so the faster content of page based results can be served instead).
No more silly tracking, just showing what someone is likely to be interested in at that moment.
In other words, use referers to figure out if they came in based on keywords from a search engine (ads targeted more towards that, but still biased to the page viewed) or otherwise just based on the content of the page.
That's it; the first can be quickly memoised across a set of common terms for a page (and while doing so the faster content of page based results can be served instead).
No more silly tracking, just showing what someone is likely to be interested in at that moment.