Here's John Markoff's account in What the Dormouse Said:
Doug Engelbart sat under a twenty-two-foot-high video screen, "dealing with lightning with both hands." At least that's the way it seemed to Chuck Thacker, a young Xerox PARC computer designed who was later shown a video of the demonstration that changed the course of the computer world. . . .
[Doug] Engelbart had chosen the annual Fall Joint Computer Conference, the computer industry's premier gather, for Augment's debut. In the darkened auditorium, all the seats were filled, and people lined the walls. On a giant screen at his back, Englebart demonstrated a system that seemed like science fiction to a data-processing world reared on punch cards and typewriter terminals. In one stunning ninety-minute session, he showed how it was possible to edit text on a display screen, to make hypertext links from one electronic document to another, and to mix text and graphics, and even video and graphics. He also sketched out a vision of an experimental computer network to be called ARPAnet and suggested that within a year he would be able to give the same demonstration remotely to locations across the country. In short, every significant aspect of today's computing world was revealed in a magnificent hour and a half.