I've just started to play around with a resource called 'Screentoaster' which allows users to create their own line screencasts without downloading any software and for free. I'm very impressed so far - I've only tried doing a really quick screencast - a demonstration of the Icerocket Big Buzz search, but it's simple, easy to use, fast and effective. I've used a voice over with this show - have your speakers turned on if you want to hear what I'm saying, but there's also an option for having onscreen captions as well. It's also possible to add in webcam too, and that's on the list to try.
I can see the value of producing resources like this - quick video screencast posts inside of just text, quick training overviews and so on. I'd be really interested in your comments.