I've done presentations and speeches as short as 30 seconds, and as long as 75 minutes, and in both cases, I always memorize and rehearse the talk, but I never

I've done presentations and speeches as short as 30 seconds, and as long as 75 minutes, and in both cases, I always memorize and rehearse the talk, but I never memorize a script. This is generally a simple concept, and I think a lot of public speakers (who are far better than I am) do this as well. The idea is that you should know what you are talking about, but it should always be fresh, new, and interesting. When I do power point presentations, this is easy to accomplish - the points (1 to 2 at most, usually) are on the slide, and I simply expand on them in my talk. I may rehearse the slide/talk 10 times, and each time it will come out slightly different, and that is generally good. I want to make sure that I know what I am going to talk about, but I trust myself to be able to discuss the topic with some insight on the spot. Granted, this only works for topics you are familiar with, but no amount of prep in the world will make you comfortable leading a 75 minute discussion on a topic that is not close to your heart and mind.