at least 2 nixos users were affected by a graphics bug that got fixed
in 2.15.
Officially 2.15 was meant for a newer xorg server, libdrm, mesa and all, but
I've been running with this for over a month with no issues (used
compositing desktop, opengl and hd video).
I know 2.17 is in the repo, but it doesn't builde (missing deps I
think).
svn path=/nixpkgs/trunk/; revision=31661
5ebdf058cc