I followed a link to a YouTube video that was supposed to be a famous lecture about giving effective lectures. Unfortunately, the video had been removed. I suspect for copyright reasons. I did a little searching and found this site through Harvard that has the lecture by MIT professor, Dr. Patrick Winston available online. It is also available for purchase if you would like a copy on DVD.
The video was made in 1997 and is a little dated in places. For example, it uses a chalk board and overheads with nary a mention of the possibilities of powerpoint. It was intended for folks who were going to become college level instructors. Still, I think it makes many valid points useful for any teacher. I have been thinking about one of his points recently as it is something I am guilty of. When we use slides (overhead or powerpoint) it can speed up the pacing of our lecture. Dr. Winston mentions that blackboards have been around for a long time because they fit the pace of our natural speaking voice. Ready made slides allow us to move quickly and dole out lots of information. often faster than our audience can process. There is a natural speed that goes with writing out key points and a drawing on a board. We need to be cautious when using technology that we don't move too fast.
Although, I do remember an Economics teacher when I was an undergraduate that came into the classroom, placed a box of chalk on the desk and then commenced to fill the chalk board completely with diagrams and graphs. He started on the right side and worked his way across the board, drawing and talking the entire time. As soon as he filled the board, he erased it, from left to right, got a new piece of chalk and then began filling it up again. He did this for an 90 minutes twice a week. If that man had used an overhead or god-forbid, powerpoint slides. My brain would have melted.
[Image: Captured from the video: How to Speak: Lecture Tips from Patrick Winston; http://isites.harvard.edu/fs/html/icb.topic58703/winston1.html