Microsoft is wrong. The particular type of social networking site known as social bookmarking might be a fad (sites such as Digg, del.icio.us), but social networking in general is here to stay. Don't think of them as websites.
Think of it as email 2.0.
Google's also on the wrong track: using peoples social networks to sell them stuff is tacky and creepy.
Also, I don't think I'd want to import all my friends from one place to another. Having different networking sites is about different circles, different groups of friends. I want my networks separate.