Parallella seems very cool. I'll probably pick one up when I have free time.
I've worked with the Zynq chip on board, which is also great. For $99 it's one hell of a dev board, considering you get an FPGA with hard ARM cores, as well as the Ephiphany chip.
The Ephiphany processor fills in the gap between CPU and FPGA tasks in my opinion. Things that would require complex state machines on an FPGA could be done in parallel on the RISC cores very easily (and quickly). I can imagine doing some image processing or something (that doesn't lend itself well to FPGAs) of the like with this.
I'll be following you guys and may have time to contribute, but I am just a hardware guy after all.