Check out this CNET article on tracking. 

Summary: Cable companies are trying to watch every site you visit so they can figure out what advertisements to show you.   http://news.cnet.com/8301-13578_3-9945309-38.html

My take: Think about the implications of this on your shared home computer.  What if you just found out about a serious health problem, but weren’t ready to share that information with anyone?  Given the example above, the cable company could show very relevant advertisements based on your searches.  If other members of your household used the home computer…that private health problem may not be so private.