A more recent trend is to use several points of data assumed to be unique to a user, in place of cookies. Your IP address, browser, UserAgent string, screen dimensions, fonts, other factors, when combined together via simple hashing, usually provide a unique identifier. This unique identifier can now be stored at a data provider and a profile can be built against you. This approach breaks down when there are people are sharing the same computer, browse from offices with similarly configured machines, or even upgrade their system. But it's still very valuable information, and with so much money in play it'll only get more sophisticated. http://www.bluekai.com/audience-data-marketplace.php