If you use Gmail, you have to install Rappaportive.
I’ve been using this software for awhile now and it is really cool. What it does is try and pull the contact information from anyone who emails you from various social media sites (Facebook, MySpace, LinkedIn, etc.). If it finds information, it will display it along the right-hand side of your Gmail window (where the ads usually appear). This includes things like their photo, location, and links to the various social networks they have profiles on. It helps to make email a lot more personal, especially when it pulls up a photo of someone you’ve never met before. It’s also free, which makes it even better.