If you're using an app you've never used before the HUD isn't going to help you at all!
Huh? That is precisely who it will help the most. You'll be able to type whatever you want to find if a menu item exists with that functionality rather than digging through every single menu and submenu.
However this system doesn't go far enough. It needs to have synonyms - some music players call it "shuffle" while some call it "random play". Additionally many items are actually on dialog boxes not menus. They got lucky with the Inkscape effects which would be unfindable if there had been an effects dialog.
I think a far better solution would be a hybrid combination of Microsoft's ribbon menu system and the Chrome preferences (chrome://settings and search field) behaviour. However this would require rearchitecting applications and user interfaces.
It seems they have to compensate for their annoying to use global menu. I don't have anything in particular against global menus, but Canonical's implementation is just horrible. Not only do they hide it (which is annoying enough) but the way how they push the menus over dbus is slow as hell. It always takes a few seconds on my (admittedly somewhat older) laptop to open a menu and on all my other systems it is very sluggish as well. It's really a shame since I actually like the unification of the title-bar and the panel (the indicators also feel great).