I first used screen-casting when I worked at Brighton and Sussex Medical School. I fear I can't remember the tool I used, a ur-Jing, to capture walkthroughs that were supposed to demonstrate to users how to navigate their way through the Scylla and Charybdis of NHS and higher education Athens accounts. Though I played around with them, I never used them for real. I doubted the extent to which medics, who need solutions that work instantly, would sit through, and recall anything, from a video demonstration on their screen. Perhaps I was wrong.
The interesting thing about constructing a screencast is how, as with any activity where one has to explain or teach something, it makes one realise how complex apparently straightforward tasks are, and how many individual actions there are in processes that, because we carry them out daily, seem second nature and automatic.