Guy Kawasaki’ n addition to being a good author/blogger, was one of the very early Apple employees and more recently has been a venture investor. At Garage, probably he has seen countless Powerpoint presentations. Presumably because he is tired of seeing poor Powerpoint presentations, he spends many pages in his book, Art of The Start talking about Powerpoint best practices.
His mantra is that Powerpoint should follow a 10/20/30 Rule (check out The Art of Pitching section in the book). There should be no more than 10 slides in the presentation as very few people take away much more than one concept from a presentation, so all that other stuff is extra. The slide presentation should be designed to last 20 minutes, leaving room for ample questions between slides or after the presentation. He says the font should be size should be no smaller than 30 (Arial font). Guy says that audiences read faster than you can talk, so that while you are up there talking, they are trying to read your slides and not listening to what you are saying.
He says that there are something like 60 animation features within Powerpoint and he recommends the less use of it the better. His advice is to use your voice & body to emphasize when a point is important, not some fancy Powerpoint trick. The only place he recommends using any of this is in going through bullet points on a slide, presumably to avoid having people read ahead. Speaking of bullets, Guy suggests that bulleted slides should have one point with bullets and only one layer of bullets (lest you violate the 30 part of 10/20/30).
Reference: Guy Kawasaki