Robin Hanson cites a recent study relevant to anyone who gives presentations. The study examined how well students retained information about the cold virus. In one experimental group the students read a packet with various peripheral details that were not very interesting; the other group read a packet with various interesting details. Conclusion:
In other words: Interesting but not-quite-essential details distract from understanding the core point.
One of the classic books in the field of multimedia cognitive theory is Richard Mayer's Multimedia Learning.
Speaking of presentations, I'm giving a free talk on January 14th at 12 noon at Foothill College (Appreciation Hall) in Los Altos Hills in the Bay Area. If you're local, come! No RSVP necessary. Email me if you have questions.