A social network that charges its users $50 a year would have been almost unimaginable just a few weeks ago, but is now a reality. A challenger to Twitter called App.net exceeded its crowdsourced funding target of $500,000 over the weekend, and will bid to make a profitable social network free of ads.

I previously wrote about App.net and its creators goals (see “A Social Network Free of Ads”). Now the project has received the money needed to go ahead, the real work begins, and the public scrutiny is already ramping up. As you might expect, many are expressing skepticism about the venture, for example tweeting that few Web users will want to pay when so many alternatives are free. Even users of App.net itself asking that it become significantly cheaper, or even offer a free tier (others vehemently oppose that idea).

With more than 11,000 people that have invested at least $50 in the project, App.net will probably have few problems in the short term. The “alpha” version of the network is already buzzing with conversation, albeit mostly about the project itself–its existing bugs and possible future features. Some third-party clients are already available, including Web services and iPhone apps at an early stage of development. 

But, as of yesterday, only 3,500 people had actually begun using the service, mostly from the tech industry. Things will get busier when the rest of the 11,000 become active, and some people with high profiles on Twitter and other social media have already signed up. British actor Stephen Fry, who boasts 4.7 million Twitter followers, is one of them:

“Looking forward to watching this service develop, grow and offer an open alternative to the increasingly commercial and controlled big guns”

Messages like that from figures with large followings could tempt more people to give App.net a chance.

A more serious challenge for the nascent network may be criticism within the tech community that App.net’s approach is not different enough from Twitter’s. Both are private companies building social networks to make money, the argument goes, and App.net just does it in a slightly different way with some strong policy promises bolted on.

People taking that line say that the Web–and wider world–would benefit more from an effort to create decentralized social networks, as well as technology that allows communication between networks owned by different companies. That’s the position of Dave Winer, recognized by some as the inventor of the blog, as well as venture capitalist Albert Wenger, who puts it like this:

It would a huge benefit to society if we can get with social networking to where we are with email today: it is fundamentally decentralized with nobody controlling who can email whom about what, anyone can use email essentially for free, there are open source and commercial implementations available and third parties are offering value added services.