I can't see how this is a "radical new idea". It's a good idea and very valuable if executed correctly, but taking an existing, proved model (aka facebook) and tweaking it to work for academics is not new and hardly radical.
I'm not hating on the idea, I love more tools for academia, but the title is hyperbole.
i thought the same thing at first, having just read the title, but it seems it's really not about the "social network" part at all. this is more like arXiv.org in that it's a platform for academics to publish their own research papers.
Have you tried actually logging in? This is not quite arxiv.org — I'd estimate that 90% of the engineering going into academia.edu has gone towards features on par with LinkedIn for their spamminess. I signed up, and was asked about 10 times to connect to Facebook, Gmail, invite my friends, etc.
They have some interesting features (such as feeds of recent articles organized by journal you can sign up for), but by far the most important feature of academia.edu is growing academia.edu.
