Both the DZ77GA-70K and Z77H2-A2X motherboards have been running fine under Ubuntu 12.04 LTS with a variety of processors. The stock Linux 3.2 kernel has been running without fault and the Linux 3.4 kernel is also obviously running well too. All functionality seems to be in place. Ubuntu 12.04 LTS is being used since it is the latest-and-greatest packages, but even going back to Ubuntu 11.10 those packages should have the Panther Point support in place. I also have not run into any UEFI problems on Linux with either the Intel DZ77GA-70K or ECS Z77H2-A2X.
Intel pushed out the open-source Ivy Bridge graphics one year ago and the Panther Point support has been around for around that long too, in some areas even longer. In early March I wrote about Intel Los Lunas 2 and Ivy Bridge already being ready under Linux. Intel has already been prepping Linux support for Lynx Point, which will be the new chipset to be paired with Haswell when launched in the next calendar year. There is also already open-source Haswell graphics code and Haswell compiler support available.
So unlike when Intel launched Sandy Bridge / Cougar Point in January of 2011 and there were some initial problems (read Intel - It Was One Heck Of A Year For Sandy Bridge Graphics), the Ivy Bridge / Panther Point open-source support under Linux is in much better shape as far as the "out of box" experience. Overall everything should be in good shape; much more extensive tests are forthcoming. I will also be exploring how well the Intel Z77 hardware and the upcoming processors work with the *BSDs and Solaris.