Around here, we've got a lot of real-life social activities that feed off social networking -- like periodic Tweetups where the local Twitter users meet in real life. I've made several good friends, met a lot of folks in real life that I probably would not have otherwise met, just because of having first "met" them online.
This is important for me, because I tend to be an introvert. I've had to force myself a bit to get out to these real-life social gatherings, but because I wanted to meet my online friends face-to-face, I made the effort.
In my case, social networking has probably made me more
social (in real life) than I otherwise would have been.