I've used CamStudio, but prefer WMEncoder 9. When it comes to documenting non-trivial computer tasks, screen capture videos get my vote! They provide many benefits to both the author and the audience by reducing the time it takes to produce, maintain, and study documentation. I've also found videos to be significantly more accurate than written documentation or diagrams. As a simple example, compare writing out the steps involved with installing an application, to a screen capture of the process. The "writer" will probably end up going through the install/uninstall several times as they attempt to document every user interaction. Not only is this tedious, but it's also very error prone. Missing and incorrectly ordered instructions are a common occurrence, which confuses the audience. Even if the "writer" does an excellent job, the written document leaves much more open to audience interpretation than the video.
The tools have come quite a ways, but they still have a ways to go. WMEncoder's fuctionality is split across several applications for no apparent reason. Things like that, and the vast number of options that are displayed in each UI scare off many potential users.