Very simple: what is the cost per year per user? app.net started with a number of users that keeps the lights on. As they grow, there is no reason the cost per

Very simple: what is the cost per year per user? app.net started with a number of users that keeps the lights on. As they grow, there is no reason the cost per user needs to go up. The price of the service guarantees profitability as long as they maintain a minimum number of users. The problem with Twitter is that they grew to hundreds of millions of free users before figuring out a business model. At that scale, the only model that's proven to work is ads.