Just to share a different point of view.

I have the c720 with arch installed. There are some problems, mainly the GPU lock https://bugs.freedesktop.org/show_bug.cgi?id=83677#c102 The bug is fixed in the 3.19rc kernel.

My main problem was the very bad build quality of the laptop it self. I'm used to mechanical keyboards, I never got used to the c720 one.. The screen is also really bad. Given the price tag it's hard to complain though.

I finally put chromeOS back and gave the laptop to my SO. I got a used x220 in perfect condition for a bit more of the c720 asking price. I replaced the screen with a new IPS bought from ebay. Best linux laptop I ever had.