Well in Keynote (the app), you can view the notes on a different display while the presentation is playing on another. So you can know exactly what to say by looking at the display.
What I wonder is:
1. Where do they put the Mac(s) that has the presentation on it? They must have a backup Mac ready to go in case something happens during the presentation to the Mac thats presenting the keynote.
2. How close to the projector is the Mac(s) placed? Otherwise, that must be one helluva long DVI Cable.
3. What kind of Remote is used? Is it radio based? IR? Bluetooth?
In fact, they must use multiple Macs to do the keynote. They have Mac(s) to present the main keynote with backups, a Mac to present the intro movies that are made, a Mac or 2 for the demo. A Mac or 2 for any Demo's that others are presenting.
I think its a ton of work for any one of Apple's 2 hour presentations, and thats just for presentation itself. Thats not counting all the hard work that goes into getting the products ready in time for the presentation.