There must be a certain sweet spot between tracking a user's browser history and having zero targeting in advertising. A niche community or site has things simple -- they need to get direct advertising from businesses in their field. A more generic web service (like Facebook) could use only the data a user explicitly provides on their profile. A site with wide ranges of content could use contextual advertising. All of these options only use data that's already available on a company's servers, and do not require tapping into browser histories through tracking cookies. The main problem with tracking is its implicit nature -- most people don't realize just how much their browsing history reveals about them, but they do understand the information they explicitly reveal on Facebook or Twitter.