> Edges and corners of the computer monitor (...) are particularly easy to acquire with a mouse, touchpad or trackball. Because the pointer remains at the screen edge regardless of how much further the mouse is moved, they can be considered as having infinite width. This doesn't apply to touchscreens, though.
But there's an argument to be made for the spatial-locality as well, as you say. I think it's an interesting trade-off / difference of design philosophy.
-A UI can't/can't-not adhere to Fitt's Law; Fitt's law tells you where to put things to make them easy to hit* it says nothing about what you should put there.
-The entire edge is infinite but if your mouse has any horizontal velocity (which is extremely common now with wide screen monitors) a top menu item is only as deep as it is long. It's still easier for being 2D but it isn't infinite.
*more accurately it's a mathematical model that tells you how long it takes to acquire a target with a mouse. I have no actual proof that speedy = easy.
Exactly how relevant is Fitt's law? Perhaps it made sense when nobody knew how to use a mouse. My screen is littered with click-able elements (hello Hypertext) and I have no problem hitting any of them. The menu in this window isn't even the most important or used element on my screen right now.
The problem with that is that Unity hides the menu items until you mouse over the menu bar (at least in 12.04; maybe that's changed since). Mystery meat is the ultimate anti-Fitts.
Of course, it looks like that behavior will be the same in this new mode, which is sort of the worst of both worlds from a Fitts' law perspective.
I think the Fitts' law issue is a bit irrelevant though. If you want to use menu items quickly, you use the keyboard.
> Edges and corners of the computer monitor (...) are particularly easy to acquire with a mouse, touchpad or trackball. Because the pointer remains at the screen edge regardless of how much further the mouse is moved, they can be considered as having infinite width. This doesn't apply to touchscreens, though.
But there's an argument to be made for the spatial-locality as well, as you say. I think it's an interesting trade-off / difference of design philosophy.