In Where Keyboard Shortcuts Win, Gruber talks about Tog’s findings on mouse vs. keyboard. In a footnote, he adds:
Especially with most Cocoa apps, where the Find commands are in a sub-menu, and thus take even longer to target using the mouse.
To me, this is a real problem on Mac OS. It is not one that Apple has not only completely failed to address, but has actually made worse in Mac OS X. For technical users, items in hierarchical menus are slightly more difficult to activate. But for non-technical users, items in hierarchical menus are not just a little more difficult to activate, but awesomely so. And in Mac OS X, Apple has introduced more of them!