Clever script that looks at your web browser history and taking the aggregate of the male to female ratios for sites that are in Quantcast’s top 10k sites determines whether you are male or female. In my case, it was accurate… to a degree that suggests I might require a little diversity in my web browsing. 
So what I did is I modified the SocialHistory JS so that it polled the browser to find out which of the Quantcast top 10k sites were visited. I then apply the ratio of male to female users for each site and with some basic math determine a guestimate of your gender.
[From Mike On Ads » Blog Archive » Using your browser URL history to estimate gender]
