The French National Institute of Computer Science just published a study, where they analyzed over 10 million usernames from various websites and social networks, finding that many people use the same or similar enough usernames across services allowing malicious bodies to build pretty comprehensive profiles of you. They released a tool to analyze the uniqueness of your online usernames. You can read the study here as a freely downloadable PDF.

The take away is to use distinct usernames for different services, and make sure you only use your real name if you want all that account info to be associated with the real you.

via [TorrentFreak] via [Cornell]