I'm running ubuntu 12.10 using Gnome 3 shell.
Xorg uses 80-100% CPU and the system isn't performing well --
OpenOffice is unusable and nautilus hangs a lot when I try to browse.
The system has 8 cores and gets really good performance otherwise ( anything not graphical ), I do most of my work from the terminal so it usually doesn't matter, but I'd like to have a more usable system. I've searched and I've been really frustrated -- I've just found a lot of "confirmed" bug reports and can't find any solutions. The only thing I did see that looked promising was for Kde though, and it involved changing how Qt handles font rendering. If it helps the problem first appeared with upgrade to Gnome3.
I know Gnome doesn't even use Qt but maybe something similar is happening?