"A long time ago, it became fashionable, even recommended, to disable
menu items when they could not be used.
Don't do this. Users see the disabled menu item that they want to
click on, and are left entirely without a clue of what they are
supposed to do to get the menu item to work.
I'm running into an interesting conversation with more regularity
every week. That conversation surrounds the usability compromise that
sometimes occurs when optimizing pages, functionality, content
organization and linking strategies for search engines. There is
theory being preached within my company that if you optimize for
search engines, then you are optimizing for the user as well. I
disagree. I think they are two separate sets of logic, that may in
fact overlap, but are absolutely not in harmony.