If you’re using Gmail and don’t have Rapportive installed, then you’re missing out. It replaces the Gmail advertisement to the right of the email with useful information:

• Profile picture
• Brief bio
• Lists all the networks that they use (from Facebook to Foursquare to Yelp, etc.)
• Allows you to easily add them to your network
• Add a private note about the person for future reference
  

P.S. It works with Google Apps.