I have spent years teaching students how to make good PowerPoint presentation. It seems to be working because their PPTs are getting better each year.
The interesting thing is that the most effective way to teach success with PowerPoint is not to show them examples of good ones. It is to show them how bad PowerPoints can be.
I just found a YouTube video of what appears to be a comedy routine done by Don McMillan. I don't use the word "appears" because it isn't funny. I use it because it looks and sounds like it is filmed in a comedy club. Don does a good job of showing REALLY BAD PPTs.