I rediscovered an old bookmark of an excellent post on copyblogger today: "12 tips for Psychological Selling". The key idea here is that any purchase is an emotional decision, facts and logic come in second. 
The blog post is written with an online copy writer in mind, but some of these 12 tips can provide useful guidelines for PowerPoint presentation design as well. Especially for sales presentations, or even VC pitches for funding a startup. Maybe not every presentation is about selling something (a product, a company), in the end all presentations are about selling an idea.
  1. People make decisions emotionally
  2. People justify their decisions with facts. Combined with 1: the numbers and stats in your presentation are probably be used to post-rationalize an emotional decision. They are not the key decision driver
  3. Peole are ego-centric: what's in it for the PERSON you are presenting to (not just the company he is working for)
  4. People look for value
  5. People think in terms of people: real-life situations, social interactions, stories are better vehicles to get a point across than logic, data, and analysis
  6. You can't force people to do anything: convince them.
  7. People love to buy, people love to be sold to: HELP THEM do what they want to do
  8. People are naturally suspicious: add testimonials, maybe even a bit of hard data
  9. People are always looking for something: love, wealth, glory, comfort. Your presentation needs to link these desires with what you are trying to sell
  10. Not really relevant here
  11. People like to see it, touch it, feel it, taste it, smell it: good pictures, good diagrams, good demo screens
  12. Most people follow the crowd, again testimonials, your customer list, etc.
Many of these concepts also are discussed in the book "Made to stick". One of the most interesting factoids in this book (if I remember it correctly) is that it is actually scientificially proven that requiring to switch on the logical/analytical part of your brain literally turns off your desire to buy into a story.