alpha.app.net, the test bed for app.net development, is improving quickly.
it's a bit hard to find, but there are now feeds for user posts and for tags. For example, here's the feed for my app.net posts: https://alpha.app.net/johngordon.
There's no feed yet for mentions, I'm looking forward to that. It will be helpful to add some of these to Google Reader for consumption in Reeder.app.
My posts to App.net are my pinboard postsprocessed by IFTT and Buffer (yeah, a real hack) then posted to alpha.app.net. So they are equivalent to my Twitter posts (except not truncated!) and my google indexed wordpress archives of my pinboard posts.
I'm hopeful that app.net will eventually what Google Reader Share might have been. In time it may become my primary microblogging platform (displacing pinboard, though pinboard has been pretty good to me).