For agile software developers, Apple's new Quicktime 10 is a great new tool. Now with a few clicks, you can demonstrate a feature or a bug by recording your desktop as easily as you might use Ctl-Shift-4 to capture part of your screen.  This is somewhat limited by an inability to record sound, especially the developer or user explaining the feature or issue at hand.  I think this new functionality is a real benefit despite the fact that a lot of video editing people have been trashing the new Quicktime 10 video utility that comes with OS X 10.6 (Snow Leopard).

A more advanced option remains the use of professional tools like Telestream's Screenflow ($99), which allows voice recording, text callouts, and potentially smaller file sizes. But other than that, it is overkill with features like sophisticated editing, transitions, and recording video of the speaker. See