You may have noticed more and more websites using facebook as a primary login method. Not only is it a quicker login process, but the use of facebook identities cuts down on spam and trolling. Facebook, and the web is changing.
Facebook is becoming the foundation of a formerly anonymous internet. Where previously, facebook facilitated interactions between members on it's internal pages; Today, facebook will enable third party social interactions, and access to third party nonsocial utilities & productivity apps.
As facebook moves toward hosting the entire internet upon it's social graph, and as your data is accessed by applications on a daily basis, it's days as a private, intimate, network used to share drinking pictures and inside jokes is coming to an end. This is not necessarily good or bad, it's just different.
For those recent grads that signed up with their college email, and posted obnoxious photos on Sunday afternoons, this is a change in mentality. Your facebook identity will become similar to the footer in your emails. It will become less controversial, and a little more business oriented,
Conversely, I believe the market is creating an opening for a more intimate, exclusive network. One that would be optimal at around ~30 of your closest friends. A network that adheres to the social gatherings and parties that your relationships are originally derived from.