I've found myself doing a lot of screencasts recently. Screencasts are great for demonstrating software or techniques when you can't show the user directly. In some ways, a good screencast is even better than a good live demonstration because the user can go back and watch the screencast any time they want.
For creating screencasts on my Mac, I use iShowU. iShowU is one of the first pieces of software I purchased for my Mac. It's nice looking and easy to use. And it has a plethora of options to create videos in many formats and quality levels. At $20, it's a steal. I only wish it had an option to make me sound more intelligent and confident. I usually end up doing several takes before I'm not appalled with how I sound on video.
iShowU doesn't encode to Flash videos for the web, so that may be a non-starter for you. I usually just end up distributing the video file directly.