Yes, it can.
Oh hell no! : ) Heh, I’m kinda known around here as the anti-JS nazi, though really my only problem with it is when devs use it as a crutch for their poor HTML/CSS skills : )
Nope, a “pure CSS” nav bar is preferred (though be aware, there are usability issues with dropdowns for some folks either way).
As Ralph said, IE6 can’t properly use one… however, they are not necessarily the ONLY folks having similar trouble with a CSS nav bar! (what do people using a touch device do, if they have no :hover??)
I sometimes add a slight onmouseoff delay so that users with shaky hands don’t get deep into a menu and then lose it all because the mouse wandered off the submenu for a nano-second (though the deeper the menu, the less usable it becomes and the more usability/accessibility problems you run into, because they are delicate things).
However, IE is over 100 years old in web years, so you can pretty safely ignore it now. (Ducks and braces himself for flame throwers.
Since I’m going ahead and supporting the .000005% of my users who may be blind and using a screen reader, I’m sure as heck going to support those who cannot upgrade their IE or use another browser (and I have almost 20% of these people, not ignorable).
It won’t say undefined, it just won’t drop down if it requires JS to drop down.
The bad menus have href=“#” in the top-level items, so without JS you don’t get anywhere : (