Ironically, I do enable them on my tablet, because I don't always have a keyboard attached to it. Tablets generally have enough space for full menus / toolbars, and lacking a keyboard they're arguably the form factor most in need of them.
I know about the "Alt" key, but I find the need to press that to pop up the menu to be incredibly annoying.
Also I miss typing ".." in the URL bar to go to my home page (I'll admit this was an iexplore quirk, albeit a really convenient one...)
Interesting. Thanks for sharing.
I use the menu really frequently -- for pretty much anything that isn't a toolbar button.
I tend not to use keyboard shortcuts generally, but particularly if I'm just reading a website -- in that situation, my hands are on the mouse, not the keyboard, and moving to the keyboard to type a shortcut is more inconvenient than just being able to use two clicks on a menu.
Edit: apparently on PCs the per-window menu is activated with Alt, TIL