Don't Hide or Disable Menu Items?

Joel Spolsky of Joel on Software fame recommend that you shouldn’t hide or disable menu items. Read the piece here. I saw hogwash.
As a user, a disabled menu item tells me something: I haven’t selected whatever object I need to perform this command. It seems idiotic that I’d want a messagebox popping up AFTER I selected the menu telling me that I didn’t have whatever selected. Talk about confusing.

The
Daring Fireball response is perfect.

Though, I dare say that there is a point to Mr. Spolsky’s observation. There does need to be some way to let users know why a menu item is disabled. Oh, it seems that Apple had thought of this already way back when with
Balloon Help. (Link from Daring Fireball).

Another excellent response to the original premise by Lukas Mathias
here. Lukas suggests using tooltips to aid users. (Link from Daring Fireball).

Thoughts? Is Joel right or is he treating the user like they’re a friggin’ idiot when they don’t need to be?