One tool I use occasionally to whip up quick demos and tutorials is Wink. I've done several quick tutorials here with Wink showing how to do basic Subversion tasks and have gotten good feedback from everyone who has watched them.
Wink is a Tutorial and Presentation creation software, primarily aimed at creating tutorials on how to use software (like a tutor for MS-Word/Excel etc). Using Wink you can capture screenshots, add explanations boxes, buttons, titles etc and generate a highly effective tutorial for your users.
Today I was surfing around and decided to see if there was a new version available and after downloading and checking out the readme - I noticed it now supports Linux!!! (I haven't tried this yet but will tonight!)
This version has been tested in Windows98, ME, 2000, XP and various distributions of Linux including Ubuntu, Gentoo, Fedora and Mandrake.
Once you install Wink and run the program, you will first have to define a new project.
Wink provides a helpful wizard which will allow you to define a region of your screen and whether you want audio. You then start 'recording'. Wink will take screenshots of your screen, either every X seconds or upon every click/mouse key. You end up with a series of screenshots which you can then go back and annotate using Wink's built in tools. You can also add/remove/reorder the captured screens. Once you are done you can export to a SWF or an EXE which you can then embed in a web page or send to someone so they can view the presentation.
While not as fancy as something like Camtasia - it is free, and allows you to quickly put together animated presentations and tutorials.