Identify - Firefox Extension
Identify is a Firefox extension that combines identities across various social network/media sites and provides you with a profile about an individual. Simply navigate to the profile page or a blog of an individual you are interested in and on Windows press Alt i or on the Mac press Ctrl i.
Download the extension from Firefox plugin site
Go to any profile page like twitter.com/glennjones and on Windows press Alt i or on the Mac press Ctrl i
Example of Identify showing Andy Budd's combined profiles.
It makes extensive use of Google’s Social Graph API to find out about which sites an individual has profiles on and then uses YQL API to collect the information.