[evilduck]

Regarding slides as reference material, I've given several tech presentations at my job, and since I have to make the presentation available afterwards, I usually include slides that make the slide deck independently more useful (either interleaved or at the end) but I don't show them during the talk. I use Apple's Keynote in presenter mode, which makes skipping over slides very seamless to the audience.

For live tech demos, I've never not had some little screw up either, so if time permits, I usually make a screencast as a backup and provide that with the slides. It's time intensive and I've often donated a lot of personal time to it, but a good presentation makes a huge difference in the support you receive.