I wrote my notes up here last time this was doing the rounds: http://41j.com/blog/2012/10/my-take-on-the-adapteva-parallel...

I'm pretty skeptical, having played with the Tilera I'm not sure it gives you enough of a benefit to warrant the extra effort. The Parallella also looks a lot like a Tilera, I do wonder if there might be IP issues there down the line.

I also still think our best bet for this kind of thing is multicore ARM systems.