I think you're underestimating people. If they do decide to pay up, and then they notice that they haven't really used it in 3 months, they will stop paying even that 75 cents a month. This will lead to a lot more than 20-30% of users quitting over time.
The 30% will start using a Facebook alternative, and then once they're all settled in, they will start poaching everyone else from Facebook, and get them to use this new "cooler" social network. When companies lose their early adopters, it's over. They just don't know it until a few years later when the negative numbers start showing up, and it's too late to fix the problem.
The 30% will start using a Facebook alternative, and then once they're all settled in, they will start poaching everyone else from Facebook, and get them to use this new "cooler" social network. When companies lose their early adopters, it's over. They just don't know it until a few years later when the negative numbers start showing up, and it's too late to fix the problem.