Nice, but in a very passive way. I just recently stumbled across Papershow (www.papershow.com/us) and am intrigued by the ability of their pen (it looks remarkably like a Livescribe, but with bluetooth and the ability to interact with PowerPoint).

I've been producing "screencasts" for some time as part of lecture courses in Maths and Physics. All you actually need is a tablet pc input device and free screen capture software like "camstudio". This does simultaneous audio and will produce flash files embedded in html documents if required.