This actually is the thing keeping me from using Unity right now. A permanent menu bar made since on a 4:3 screen. But in 16:9, I just don't want to lose my precious vertical screen real estate to a menu bar.
I don't really care where the menu items are. If the top bar would auto-hide, I'd be fine with it. I just don't want to give up the space.
Apparently there's a modified Unity called "Unity Revamped" which adds autohide as an option to CCSM, but it's a slightly older version of Unity, and for whatever reason I can't downgrade to it.
Or if you have 2 or more windows vertically above each other, you even gain some vertical screen real estate.