Recording a desktop computer screen to a movie is useful for recording user testing sessions, as well as making demo videos for presentation or posting on a web site.
Here is some software for recording screencasts.
Wink for Windows & Linux, generates Flash videos. Can include annotations and callouts.
Camtasia Studio for Windows, generates AVI and MPG videos. Lots of options, very powerful. You can download a 30-day trial version of Camtasia 5. We also have a license for an older version, Camtasia 4.
Snapz Pro X for Mac, generates Quicktime. $70.
iShowU for Mac. $20. Free trial version records 30-second videos.
Copernicus for Mac. Free.
Screencast-o-matic for Windows, Linux, Mac. No install needed -- records with a Java applet in a web browser and hosts the resulting video on their public server. Somewhat frame-rate-challenged.