MATE Desktop has reached version 1.4.2. It brings some improvements and for me, it now runs far far more stable than its previous versions when I tested it on the Ubuntu 12.10 Quantal Quetzal.
All good but still, we can't use the original default Ubuntu's Ambiance theme in MATE. And so, just for fun (but finally working good) I made a fork of Ubuntu's Ambiance Theme dedicated for MATE desktop and I called it Matembiance Theme.
Download the deb HERE, and install it manually by terminal or by gdebi :
sudo dpkg -i matembiance-theme_2012.12_all.deb