Does social networking sites provide a sense of community or cause social isolation?

Question From User - Answers in Comments.

I am doing an essay for media studies and i want to know what you all think about social networking sites. Do you think they are good or bad?
Provide personal experiences if you wish, i just basically want to know do you think sites such as facebook etc are bringing us all together or isolating us all because we are sat on our own computer in our rooms.
Please reply thanks x