What info does the Google Social Graph have on your email address? If your email is publicly associated with various social networking sites, you can easily tell by entering the following into your browser’s address bar:

http://socialgraph.apis.google.com/otherme?pretty=1&q=[your email address]

For example, as of this writing, a search on my email lists my profiles for Facebook, Twitter, Quora, Google, and two of my blogs.