Well despite that fact that everyone talks about it, no one really seems able to define what it is. The best I can make out from the replies here is a fancy profile page and some mysterious changes to the buddy system (no actual details). I guess such things might be useful to someone, but not things I would say I'm desparate for.
Social Networking is just a concept really. MySpace, Facebook, Livejournal, MSN Spaces, Blogger, Ebay, YouTube, Yahoo! Groups, Epinions and every existing vBulletin forum are really examples of social networks. Each implements it in a different way.
One could argue that MMORPGs (including simulations like Second Life) and IRC are social networks as well. They don't get included because they don't use the World Wide Web. However any application that allows social interaction among its members falls into the broad definition of social networking.
With vBulletin, people are limiting their ideas of Social Networking to mean enhanced profiles with comments on those profiles and links to blog entries and images. But really the concept it much broader than that even. This perception is because of how MySpace implemented their network with friend's lists, private messaging and so forth. vBulletin already has friends lists, private messaging and a most the elements of what makes MySpace into MySpace. However some of those elements are underutilized and that is what the "Social Networking" component will enhance.