Fedora 18 is released with support for MATE desktop. For previous release one had to install MATE from third party repository. Whereas with latest version you can get MATE support with single command.
To install MATE
yum groupinstall MATE
Like me if you are not willing to use Gnome 3 at all, you can remove gnome & install mate with following commands. First of all switch to init 3 or shell using ctrl+shift+function_key
yum groupremove GNOME yum groupinstall MATE