I'm using gnome-shell and all seems to be good but I've only one problem. Nautilus seems to be very slow only when I use the theme "Faenza", with other theme is all great. In particular Nautilus is slow when switching from one Nautilus window to another the gtk is slow to load and i have to wait about 1-2 seconds before the right colours are shown.
How can I fix it? Has anyone had problems like this? I'm using Ubuntu 12.10, Gnome-Shell 3.6.2 and Nautilus 3.6.3.
Use the Ubuntu tweak's janitor tool to clean the old packages, icons and cache from cruft. It could be because of too much cache. Your problem is very unique and is not an general issue. Try my suggestion it might help