I've read the question 5 and its answers about global menu superiority.
I would like to emphasize this:
- I've been using Macintosh, Unix workstations, MS PC (DOS,Win3.1 up to Win8), Linux PC with various WM/Desktop, etc.
- Global menu was fine for me on Macintosh Classic 9-inch display, for any task.
- Global menu is painful and irritating on 24-inch display, for most of the creative tasks.
I suspect that this is not only a matter of how long the cursor travel though the screen, but also about how much you have to adjust your gaze on the area requiring your attention.
Fitts' law fails to address that point, even if you can do things quicker it might not be as productive if it's uncomfortable and tiring.
Regarding GUI, Apple has failed on several points with nowdays huge displays, for instance it tooks them years to allow window size adjustment on any border (instead of a tiny triangle on bottom right). The feature comes with Lion in 2011... That's a shame.