I think anyone who uses social software wants Priv3: Practical Third-Party Privacy, especially as tracking by these outfits seems on the rise:
How Priv3 Works
Blocking simple "web bugs" or "trackers" is fairly straightforward, because doing so does not harm your web surfing experience. By contrast, completely blocking social networking features is counterproductive, because doing prevents you from actually using these features—say to leave a comment, or to "like" something—when you would like to do so.
Therefore, Priv3 does not block third-party interactions completely. Instead, it selectively suppresses the inclusion of third-party web cookies when your browser pulls in content from the social networks, but does provide them if you decide to interact with the social networking features. You still see the number of "likes" the page has accumulated on Facebook or the comments other people left using Facebook’s discussion mechanism. Facebook however only learns the IP address of the computer you are using.
Should you decide to interact with the social feature, Priv3 detects any mouseclick or keystroke directed at the feature. It then reloads it with your session cookies and passes on the click or keystroke, thus revealing your identity to the social network and informing it of your desired action.
Priv3’s Currently Supported Social Networking Sites
Priv3 currently understands the interactive features of the following social networks:
We will expand the list in the future, as needed.