We're talking social all week this week on Talk Mobile, and one of the newest pretenders to the throne is App.net. It's a more interesting proposition than just a mere social network, positioning itself as a platform and inviting developers to build on it. It's also not free, which from the outset may have put some folks off trying it out. There are now invite-only, free, limited accounts to get people through the door and trying it out. And of course, the iMore team, well some of the iMore team, is on App.net as well, so here's how to follow us!