Harry Pierson has a blog entry on the fact that one should not read slides but rather present from memory / dynamically.  While I agree with Harry in general principal, I have to add a bit of an addition.

Using PowerPoint slides has three major advantages over doing it raw, in my opinion.  One is that you do not forget what you were going to say, but having the slides is sufficient for that, it does not mean that you have to read from them like a human text-to-speech engine.  The second advantage, that is more unique, is that PowerPoint slides can be sent to the audience before or after the presentation so that they have them as a resource.  Unfortunately, drawing on whiteboards does not have this capability.  Finally, PowerPoint scales to large rooms better than whiteboards.

Thus I suggest a slight twist on PowerPoint that I used when I was an evangelist (for those who do not know, Harry and I worked together as evangelists).  I had slide decks that kept me on task but I also included blank slides with good notes in the notes section.  I would then use my Tablet PC for the presentation and draw on the blank page as I would a whiteboard.  It led to the same sort of dynamic feeling as using a whiteboard, but it scaled to larger rooms and led to persistent diagrams.  I was able to save my Ink drawings and send the whole deck, including the Ink, to the audience.  As far as I am concerned, Ink in PowerPoint is the second-biggest use of the Tablet PC (the first being unobtrusive use in meetings).

If you have access to a Tablet PC and do presentations, I would strongly urge you to give this technique a shot sometime.