Back in 2003, I was one of the people who spoke at the first MIT Spam Conference. One of the other speakers was Paul Graham. At the time I didn't really know who he was, other than the fact that he had written A Plan for Spam which used similar techniques to my own POPFile email processor. But I only remember two talks from the conference: Paul Graham's and another by Matthew Prince.
The striking thing about these two presentations was that they didn't (or hardly) used any slides at all. Paul Graham simply stood there and read the text from Better Bayesian Filtering and Matthew Prince used extremely simple slides that mostly had headlines on them; at one point he showed a graph illustrating the ineffectiveness of anti-spam laws. It's interesting that I remember both these talks because I'm convinced that the lack of slides made my brain work in a different manner that enabled me to absorb what was being said.
The other great thing about that conference was that presentations were limited to 20 minutes including questions and that rule was rigorously enforced. Some presenters did their best to flash up as many fact filled slides as possible, but Graham and Prince did something different: they used their time well. Graham and Prince made me concentrate on their words and themselves; I remember both.
Looking back at my own presentations I see how I've used PowerPoint to ill effect over and again. I've come to loath PowerPoint (and any other presentation software) more than pie charts because I've seen it abused (and it typically is abused) over and again (in the past I ranted that It's as if Charlie and Lola is the high point of our education).
1. People jump to use PowerPoint before they think. I've seen many a presenter start by typing ideas (half-formed and ill-informed) into PowerPoint and then 'crafting' (yes, that's the word they use) to form a story. This doesn't work. If you want to make a good presentation you need, above all, to step away from PowerPoint and think about what you are going to say. You might, then, be tempted to use presentation software to get that message across, but you don't have to.
2. People use slides as a measure of success. I've seen presentations outlined in PowerPoint and then filled in. The measure of a good presentation turns out to be the completeness of the slides and the number of slides, not the content itself. I've seen people be content with a slide when its content was poor because it was necessary to have a slide on a particular topic.
3. People focus on pictures and not words. Sometimes pictures are great, Matthew Prince's graph showing that anti-spam laws were inversely correlated with spam volume was impactful because it was about the only slide he used, but mostly pictures are a distraction.
If I were CEO of a company I'd enforce a three slide rule. If you are going to make a presentation you are allowed three slides (any more needs CEO approval) and so you need to spend your time thinking about what goes onto those slides.
Above all, what presenters need to do is write. The folks at 37 Signals make a point to hire good writers. If you write your presentation first, as prose, you'll then be able to clearly see what needs illustrating. If you start illustrating then everything will look like the same presentation you've seen a thousand times.
If you hear someone say "I'll put some slides together", the correct response is "No, write a text document that says what you want to say". Only once you know precisely what you want to say should you illustrate it. Otherwise, it's like writing the introduction to a book before you've written the book.