Right now Facebook is beating MySpace, according to ComScore. Social Networking is very much a part of life these days, and while older networking sites may have to make way for the latest cool site, networking itself is here to stay.
I do believe that a library presence in the place where our younger patrons spend a lot of their time can only be a good thing, as long as it is done correctly. I agree with Meredith Farkas that one of the most important ingredients would be user feedback and ideas.
There is even a virtual library in the virtual world, Second Life, where it is being used to promote librarianship and reading.