While we're on the topic of slides, read Edward Tufte's "Cognitive style of PowerPoint". It is short, cheap and sweet discussion about all he sees wrong with most powerpoint (or keynote or libreodfice) presentations.
http://www.edwardtufte.com/tufte/powerpoint
And here's his sample:
http://www.edwardtufte.com/bboard/q-and-a-fetch-msg?msg_id=0...