A Jef Raskin followup project to the Canon Cat is Archy: http://en.wikipedia.org/wiki/Archy Fascinating UI concept: largely search-based, with everything persistent (no saving), infinite non-windowing work area, and many other interesting features.
> Every action should be undoable, even after a document or application has been closed and reopened.
At first, this sounded ridiculous. Undo after a save? But then I realized I do that now & then myself, using a version control system. So here I am editing a DVCS-managed document. Pre-save undo is handled by the editor, while post-save undo is handled by the DVCS (which is nice, but I usually have to look up how to do it).
All this underscores what crappy interfaces we really have, and how we get used to them, and so overlook their serious flaws.