Following the posting on Michael Deutch's 10 tips for better presentations using mind maps, (http://vismap.blogspot.com/2009/02/10-steps-to-great-presentation-maps.html) you might want to see another take on the dangers of using PowerPoint (or any other presentation tool) badly. The material is by Edward Tufte, who you may be familiar with as a design expert on the presentation of information.
Taken from the introduction to an essay on PowerPoint, Tufte writes:
"Alas, slideware often reduces the analytical quality of presentations. In particular, the popular PowerPoint templates (ready-made designs) usually weaken verbal and spatial reasoning, and almost always corrupt statistical analysis. What is the problem with PowerPoint? And how can we improve our presentations? "
It's also worth following the link on "Rocket Science" to see what Tufte makes of the impact of PowerPoint on decision making leading up to the Columbia Shuttle disaster.