Hi=) as far as i heard Parallella runs linux kernel on Zynq ARM core ONLY and Parallella cores act as a co-processor. So you can't get all its fancy cores out of box=(( you'll probably need to make some extreme kernel + openjdk hacks (and may be a lot of others). 
The main problem is that system runs on ARM core and Parallella cores are actually OpenRISC cores and i think that linux is not ready for such multiarch system, but I hope someday it will.
I wanted to get some Parallella boards too, but for my needs maybe couple of Beagle Bone Black are more appropriate=) It's an ARM Cortex-A8 dev board with 2 1GHz cores, some 3d accelerator, 512MB DDR3 RAM, 2GB integrated eMMC storage + microSD slot, LAN, USB host and micro USB client for power and external PC control, microHDMI and audio through that HDMI, and a lot of GPIO and other pins. Doesn't have so many cores but 45$ only and it may run gentoo=) Perfect for scalable OSGi/JEE home cloud.