Plus One Analytics has an excellent post on something I totally missed out hearing at last month's Emetrics Summit in DC or this week's Ad-Tech NYC 07 where behavioral targeted ads are now using data from ISPs to track users and server ads wherever they go on the web, not just in an Advertisers' network.

"..NebuAd, on the other hand, partners with ISPs so it can observe consumers no matter where they travel across the web. It collects that data and uses it to serve targeted advertising based on where else the consumer has shown interest."

I always suspected this could be done.