I just got my board running last night based on these instructions:
http://www.parallella.org/create-sdcard/My board came, i think about ~2 weeks back, but I spent some time carefully getting all the recommended accessories I needed from this forum & thankfully it ran on first boot!!
With that being said, Next I would LOVE to get Gentoo running on my Parallella - assuming that Gentoo will compile & optimize for this boards hardware & idiosyncracies - please feel free to reach out to me if you need help experimenting with getting it Ported or what not but disclaimer, Ive been using Arch Linux a lot but am a noob to Gentoo...