Disable (and Document) Menu Items

Joel posted a short article: Don't Hide or Disable Menu Items. I think it's bad advice.

Consider Paste or Undo. If you click the Edit menu, you can tell from the enabled state of the Paste item whether or not there's something on the clipboard that can be pasted. Same with Undo. If Save is disabled it means there have been no changes since the last save. The enabled state of these items conveys information.

I'd rather click Edit and see Undo greyed out, than click Edit, Undo, and have a dialog pop up telling me that there's nothing I can undo right now.

It would be nice if your Help system included a description of all the menu items, and when they are available. An lot of the documentation I've seen includes descriptions of menu items that add no information ("Undo: Undoes the last operation") and leave out valuable information like under what circumstance that item might not be available.
It's unlike Joel to post bad advice. Perhaps he need a little SEO and posting something obviously wrong would be a great way to get a lot of people to link to him with corrections?