I don't know how relevant this is or not but I heard that Unity has the lowest OpenGL performance benchmarks.
So I switched from Unity to Gnome 3 (I'm on 12.04 too)and not only was I finally able to alt-tab out of Heroes of Newerth but I did notice that game was running at a much more stable FPS. Plus, I'm kind of grooving on the design of it now.
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