Unity has never done it for me, and on my hardware it has not performed as well as I would like.
edit: a google search of unity doesn't show it with a menu bar for file, edit etc anchored top the top of the screen like OS X, those menus are still in the application window.
I'm an Enlightenment user when not at work, so maybe I need to create a E19 fork (I wouldn't know where to start).