My personal definition of social networking is; something that helps keep people connected with their contacts. In theory it sounds like a brilliant idea. For example: when friends move apart and go their seperate ways, then can still stay in contact with minimal effort and in frequent doses. However it becomes a problem when people start to use social networking as a primary means of communication, to the point of actually being anti-social. 'Social networking addiction' is a very real concern that is affecting the both the young and old.
Personally I don't have too much contact with a whole lot of different social networking sites. I've used Myspace and Facebook. To judge whether it is an enchancement or detriment to a person's lifestyle is an invidiual thing.
In order to stay in contact with busy friends during our busy lives, posting some family photos to the relatives, I think social media sites can be an amazing thing. However if you spend every waking moment of your free time updating your status; rather than actually communicating with people, you have an addiction. An addiction that may even lead to social awkwardness and anti-social behaviors later down the track
In conclusion, a line must be drawn. Social networking should be a tool used to communicate with friends that you can't go and meet. It should not be used as a primary medium of communication