The Atlanta Journal Constitution has an interesting article on internet identity tracking. They touch on the usual subjects, identity theft, increased risk of violent crimes from the data being freely available, etc. However, what struck me as most alarming was the on at least one companies report they list things such as sexual practices. For the guy the article was about, this company gave him a score of 73 and stated he had a "tendency to cheat." Of course, they guy was married for 18 years and while he claims never to have cheated, the reporting agency refuses to disclose how they created that profile.
This doesn't really surprise me, as the greatest use of this type of information is probably to assist private eye detectives in divorce proceedings. If you can come back with a reported "tendency to cheat" you creat more work for the private eye, who in turn uses you more.