I have seen a lot of people making linux screencasts and tutorials for linux and some have a live webcam in the corner of the screen which I feel is a nice personal touch when giving people advice.
However there is little or no documentation on how to do this so many people just leave cheese (a webcam program similar to photo-booth in mac) open in the corner but this takes up excess space. Some people advise you to do it through mplayer using a command but this takes time to work out the correct parameters for your webcam.
There is an easier way.
Gmplayer (Gnome Mplayer) has an option to do just this.
In Gmplayer you can simply go to "File">"TV">"Open Analogue TV" and it will usually display your webcam.
There are of course other media players that can do the same. VLC player for instance can use and record a webcam via the capture device menu but in my experience G-Mplayer works best.