An addendum to yesterday's post - ICA:UK, a reliable source of materials and training on highly participatory facilitation, has summarised 10 principles to prevent online fatigue. I've been using all of them. They work.
At any rate, avoid text-filled slide shows with voices droning on in the background! Visual aids are great, but if you just show pages and pages of text that you read to your audience, they'll end up muting you and joining a different event on their other computer. I admit that was what I did in a recent conference full of half-hour text-rich presentations by invisible voices. I couldn't help it. Since the different conference followed the same mode, I still felt I would have been better off reading an article, in my own time, at my own (rather energetic) pace.