That is because Hiro's comment makes no sense. Social networking has been around long before the internet, the coining of said term or even writing on cave walls in France. It's basis for pretty much everything we do in society.
Will social networking websites like MySpace and Facebook fall like Live Journal, Friendster, Six Degrees and all that came in between? Most likely, but another will be there to take its place. Both do seem to be doing a significantly better job on improving the experience and options for web users as the internet grows more complex. It looks like the web might have grown up enough to allow these two sites in particular to keep evolving with the times so a new idea for web-based social networking won't be as easy to usurp these sites like they did to others in the past.
The problem with sites like MySpace or Facebook, is that they got so damned cluttered, and at least Facebook is trying to reverse the trend, by relegating apps to another page. MySpace is still awful though, even with a fast Comcast broadband connection, loading a typical MS page kills just about any browser/computer I'm on - Safari/IE/Opera/FF, doesn't matter.
I've never been that big into personal blogs, but FB is cool to keep in touch with friends from HS and my various colleges. I'm more into having a site to post pictures however, and I like Picasa a lot for that.