According to the consensus (and loosely following the Google spreadsheet I created for that purpose), I have removed the Demo directory from py3k. Most demos have been deleted; some have been moved into Tools or into the docs as an example. If I removed something you think should have stayed, please speak up.
I kept a few less-useful ones in a new directory called Tools/demo that aims to give a broad overview of what you can do with a few lines of Python. Please feel free to remove and/or add demos there, if you find better ones.