>>aculve+(OP)
The reason I think App.net is going to grow is NOT because it doesn't have ads or that the "users are not the product", etc. It's because the community it hosts will be so tightly grouped around a similar, passionate interest: tech startups. Requiring payment, being called "App.net" (they'll be tempted to change this), and being distributed via word of mouth amongst the segregated tech startup community, will prevent so many different types of people from using it. This is all a great thing and I bet there will be opportunities for other "Twitter for ________" ventures. Charging for a service like this that caters to a much smaller market makes it sustainable.
Congrats to Dalton and all involved. This is one of the most interesting and courageous internet projects in recent time.