I use an ATi card with proprietary drivers, and now using Mint 13 Cinnamon. And it goes well but ...
Sometimes ATI video driver hav some issues with Muffin, far better than first versions, but still have some issues.
Having the choice of EASY switching from config settings to metacity as default windows composer would be great for AMD GPU users.
You are working in Cinnamon 2d with metacity optional, it would be a little adition to the Cinnamon 3d config menu.