You make a reasonable claim. Lets consider the evidence though.
" there are many more people on facebook than networks like myspace ever had. This makes a transition much, much harder."
Have you considered the cost to move a single community? Facebook has a lot of users but it also has a lot of communities. So the durability will be determined in part by how interconnected those communities are. So for example if everyone in your school is on Facebook, great but who else is on Facebook that you share with? If its nobody then the 'school' community is independent of the greater Facebook user base for you, it could move en masse to another service and the members would continue to be well served. Now do you have college friends and church friends and work friends? If so then you've got a more complex social web and moving to a different service for your college friends means you now check two services instead of one in order to keep up, that is a 'negative' on your part and if enough people in a community have this same constraint then the community is more tightly bound to Facebook.
Because of that reasoning I'd claim that it does not matter how many people currently use Facebook, rather it depends on how difficult it is for an arbitrary community to move to a new service. If movement is easy (or becomes desirable) then you could see mass migrations.
"facebook is not only used for facebook, but for many third-party apps as well. People will keep their facebook accounts so that they can log in to external services."
This is clearly a 'stickyness' mechanism that Facebook has implemented for the reason you state. If you log into a bunch of places using your Facebook account then having a Facebook account is important, and leaving Facebook is 'hard'. Clearly this is in the interest of Facebook and the reason they offer the account connecting APIs that they do.
There are two potential problems with this however, one is that Facebook is less willing to reciprocate with data access to web sites that use their APIs (see the Google / Facebook problems as exhibit A) which makes that linkage less desirable to the third party. If it is a big enough problem they will drop it.
The second problem continues to be the profiling problem which is that Facebook knows a lot about you and this simply adds to their knowledge. As people become uncomfortable with that they may choose not to use Facebook login even if it is available for just that reason.
It will be interesting to see how durable these defenses are against defection. I don't doubt for a minute that Facebook will die at some point. The question though is will it be be 10 years from now, or 20, or 5. If you look at companies that have spanned several generations there is a more fundamental value proposition at work than 'friends.'
" there are many more people on facebook than networks like myspace ever had. This makes a transition much, much harder."
Have you considered the cost to move a single community? Facebook has a lot of users but it also has a lot of communities. So the durability will be determined in part by how interconnected those communities are. So for example if everyone in your school is on Facebook, great but who else is on Facebook that you share with? If its nobody then the 'school' community is independent of the greater Facebook user base for you, it could move en masse to another service and the members would continue to be well served. Now do you have college friends and church friends and work friends? If so then you've got a more complex social web and moving to a different service for your college friends means you now check two services instead of one in order to keep up, that is a 'negative' on your part and if enough people in a community have this same constraint then the community is more tightly bound to Facebook.
Because of that reasoning I'd claim that it does not matter how many people currently use Facebook, rather it depends on how difficult it is for an arbitrary community to move to a new service. If movement is easy (or becomes desirable) then you could see mass migrations.
"facebook is not only used for facebook, but for many third-party apps as well. People will keep their facebook accounts so that they can log in to external services."
This is clearly a 'stickyness' mechanism that Facebook has implemented for the reason you state. If you log into a bunch of places using your Facebook account then having a Facebook account is important, and leaving Facebook is 'hard'. Clearly this is in the interest of Facebook and the reason they offer the account connecting APIs that they do.
There are two potential problems with this however, one is that Facebook is less willing to reciprocate with data access to web sites that use their APIs (see the Google / Facebook problems as exhibit A) which makes that linkage less desirable to the third party. If it is a big enough problem they will drop it.
The second problem continues to be the profiling problem which is that Facebook knows a lot about you and this simply adds to their knowledge. As people become uncomfortable with that they may choose not to use Facebook login even if it is available for just that reason.
It will be interesting to see how durable these defenses are against defection. I don't doubt for a minute that Facebook will die at some point. The question though is will it be be 10 years from now, or 20, or 5. If you look at companies that have spanned several generations there is a more fundamental value proposition at work than 'friends.'