I like the idea. As a developer, it's certainly a more tempting business model than worrying about selling ads. The only web app I know of that does this is pin

I like the idea. As a developer, it's certainly a more tempting business model than worrying about selling ads. The only web app I know of that does this is pinboard.in. They charge a one-time signup fee, and that fee slowly increases as the amount of users increase, so the earlier you sign up, the cheaper it is (http://pinboard.in/signup/ http://pinboard.in/signup/). I don't know if it's sustainable in the long term though.