Students in the University of Washington Computer Science project have created "ShareMeNot," a Firefox Add-On that defangs social media buttons like the Facebook "Like" button (and others) so that they don't transmit any information about your browsing habits to these services until (and unless) you click on them. That means that merely visiting a page with a Like or a Tweet or a +1 button (like this one) doesn't generate a data-trail for the companies that operate those services, but you still get the benefit of the buttons, that is, if you click them, they still work. Smart.
ShareMeNot is a Firefox add-on designed to prevent third-party buttons (such as the Facebook “Like” button or the Twitter “tweet” button) embedded by sites across the Internet from tracking you until you actually click on them. Unlike traditional solutions, ShareMeNot does this without completely removing the buttons from the web experience.
ShareMeNot (via Schneier)