Unfortunately, you are among a small number of users who actually use keyboard mnemonics. In my 20 years as an interaction designer, the only users I’ve seen who regularly use mnemonics are software engineers. Most users are accustomed to moving back and forth between mouse and keyboard and aren’t usually engaged with activities that have them at the keyboard for hours every day (unlike someone, for example, who is writing code).

That said, I do think that there are some applications that benefit from being keyboard driven, especially data entry intensive applications. Watching airline attendants check in passengers is a vivid example of an interface entirely driven without a mouse. My experience working with users in those environments, though, is that they prefer to rely on arrow keys, tabs, and enter keys rather than mnemonics… and the design that I’ve shown could certainly support that.

When a menu has twenty or more items, it’s likely extremely difficult to come up with an appropriate {Alt} key letter for a particular menu item.

Perhaps the solution might be more menus but this becomes a challenge when an application becomes so powerful and complex that there just might not be enough room on the menu bar for enough menus to display all possible menu items in a single level.

For those of us who adopt keyboard shortcuts, flyout menus are much more user friendly.

The only thing that I see needs exploring is scrolling. What if the menu is too big for a netbook? Do we scroll vertically and horizontally? Of course it’s a code thing, but dynamic re-columning would be great to prevent 2D scrolling.

And what if a “sub-menu” just has too many repetitive options (eg Google Chrome’s Encoding menu)? You don’t want to display them all. Maybe a scroll box inside the menu? Or a pop-up control?

Show more than a few items at once, and you’ve lost the ability to assign meaningful shortcuts to every item.