While I like the bravery of trying something new in the GUI field, I think there's some overshooting in Ubuntu Unity.
Merging the menu bar with the title bar can save some screen estate in full screen applications:
look at this maximized terminal window.
A full row is gained by merging the menu and the title, and the menus are accessible as before: by going up and pressing the right mouse button.
Problems arise when using the terminal at its native size and get worse if you put the window in the lower half of the screen: to access the menu you have to travel up half the screen with the mouse.
I'd propose to keep the menu bar attached to the window while not in maximized mode.