If you want to keep in contact with friends who play games on different platforms, then Raptr has the answer to keep in touch and compare achievements.  Raptr is a free social networking website and computer program targeted towards video game players.

Raptr is similar to other social networking websites. Users can add video games to their profile, as well as track game play time and achievements, share reviews, game related information, and game activity.  Raptr lets users publish their gaming accomplishments to sites like Twitter, FriendFeed, and Facebook.

The Raptr client, which is a downloadable application for Windows and Mac, allows you to keep in connection with friends and allows you to see what they are playing across game platforms like Xbox Live, Playstation Network or PC. It also includes other features such as game/achievements tracking, in-game overlay, and game management.

Part Twitter, part Steam community, and part Facebook, Raptr is a social network that gives gamers a place to connect with one another over the games they frequently play.— PCMag

I have found this service to be a great way to keep in touch with friends on other platforms.  The website will amaze you with your personal game stats as well.

The Raptr website is http://raptr.com/