I just realized that Skype translates the substitution idiom "s/this/that/" into an actual edit of the previous message. Cool.
The Mother of all Demos, available on Google Video:
If, in your office, you, as an intellectual worker, were supplied with a computer display hooked up by a computer that was alive for you all day and was instantly responsive to every action you had, how much value could you derive from that?
How did I not already know about such a revolutionary event?