It's an interesting theory though: critical mass matters less to users (in a business sense - obviously it matters from the expectations of community standpoint

It's an interesting theory though: critical mass matters less to users (in a business sense - obviously it matters from the expectations of community standpoint) than it does to other potential partners. The user expectation of Twitter is that it will remain free, but maybe it's worth something to Tumblr and FB to have access to that mass. If successful, it can get very interesting from a business perspective.