I use Camtesia. I just starting using it so I don't know all the bells and whistles yet. However, it seem that it is not possible to record your whole screen becuase it slow down the update rate of your monitor i.e. it takes a while for your to see when you move your mouse or type text. It also is a CPU pig. That said it works well enough if you just keep it focused on a portion of your desk top.
A four hour video is about 75mb, and larger if you record audio.