I was just searching for a review on Yelp and I saw these (Useful, Funny, Cool) evaluation tags for a review. I was able to mark them even when I was not logged in, still they would retain the way I marked them even if I open a new browser window, or a private browsing session.
How is this done? I mean how does it track user activity without requiring me to login/signup? I don't know if its cookies or the site stores my IP address or a combination of both?