Ideally, any website should not be able to read the the history of sites that a user visited previously. Even Google is not capable of tracking the previous sites a user has visited. But a small CSS hack and some spicy Javascript is just enough to use a trial and error method to find out if a user has been to specific websites.
Mikeonads came up with a script that is using this method to estimate if the visitor is male or female. The Javascript makes use of the Quantcast Top 10K websites and the male:female ratio that they provide plus a neat algorithm to compute the percentages for male and female likeliness.
Mine turned out 50/50 
because I have switched off my history !! Good luck and let me know what the script thinks about your gender 
The same principle could possible be used to display targeted advertisements. Have been to a lot of parenting websites lately? How about parenting ads? Like sports? How about an ESPN subscription? It’s a bit scary, don’t you think? But not to worry as of now, without running the javascript, your privacy is still maintained.
Raju PP is the founder-editor of Technically Personal, which is one of the most widely read technology blogs on the web. He holds an Engineering degree in Electronics & Communication, and has previously worked as a Technical Specialist in Banking Software domain.
Pretty nice site, wants to see much more on it!
interesting! i really wonder their algo on this one. ^_^