Peter J would probably find this one useful, as would my boss. If we could enter a redline mode, where nothing in the model, sheets, views etc could be edited - and you could add notes, sketches, etc etc all very rough and freehand over the top of any view. Any views that had been Redlined would appear in red in the project browser.
When you come out of redline mode, all redline will dissapear until you go into that mode. if it were assigned to say "F5" or something, you could flick it off and on in the view to check you had addressed all comments.
I would use this myself to add notes and comments as I worked, as well using it to get comments from others involoved in the project. Would be really useful......