I wonder how many people around here are using Linux... but if you are one of them, I'd suggest using:
recordMyDesktop (http://recordmydesktop.sourceforge.net/about.php)For Debian/Ubuntu users it's available as a binary package gtk-recordmydesktop
The tool is really simple but allows you to record a rectangular region of your screen as well as set a number of settings related to quality and CPU usage during recording.
The user guide is really short, but let's just say you start recording by left clicking the icon in the system-tray
Clicking again stops the recording and right clicking pauses. Right clicking the system-try-icon while it's not recording shows a pop-up menu that allows you to select a region for recording. More advanced settings are available from the window-gui thingy.
My laptop is not very fast with a 1,6 GHz processor, but I still wanted to try compression on the fly so here are the settings I used:
video quality = 25%
no sound
frames per second = 10
encode on the fly, quick subsampling = enabled
zero compression, full shots at every frame = disabled
And an example video showing my mono time beating Seism
