When you're hoping to connect with an old friend or an old colleague, social networking sites can help. There's no denying the popularity of social networking sites has increased significantly in recent years. Now, in addition to staying connected via these sites on your PC, many social networking sites are also offering mobile applications. LinkedIn is one such site. The professional social networking site currently offers apps for various mobile devices including the BlackBerry, iPhone, and Palm handsets. A Windows Mobile app was also added recently. These apps let you keep tabs on your connections from your mobile device. The social networking site also offers a mobile version of its website at http://m.linkedin.com.Follow me on Twitter.