that's an interesting perspective, but I don't think is really valid. People will easily/hardly change their default social network but really easier than switching from Google which is a point of reference to those who are used to it. Even if you tried to switch from Google, how many are the alternatives? Like you said only two. And whenever I tried them they never make me stick to them.
And this is easier to happen because more people can build a community than a search engine.
I disagree.
As months go by, it's going to be even harder for anyone to come up with a social network as big as FB. Why ? FB's critical mass!
As it's been said, all that differentiates Facebook for an individual user is the presence of that users friend’s on Facebook — which forces them to use Facebook to connect with them.
And this is precisely why FB is not a founding member of the OpenSocial foundation. Facebook is threatened by OpenSocial’s ultimate aim of connecting user profiles and enabling users to easily manage and port their data across any social network.
And this is easier to happen because more people can build a community than a search engine.