I imagine that it won't be an all inclusive social networking site- it will instead, be a collection of sites that focus on single features (work, education, social groups, hobbies and so on). People are going to just grow out of this everything model- especially those that have been using it since high school (even grade school). There is something to be said about staying in touch with people from your past, but realistically how much does one have in common with an acquaintance from 15 years ago? I would venture to say that even the most active facebook users reduce their usage within the first few months and this trend continues as one transitions out of being a student.