Solid advice. When we started http://thinkcode.tv we immediately asked the question, will people be willing to pay for screencasts? The existence of other companies selling screencasts, like PeepCode, PragProg, Lynda, VTC (and many other emerging ones) reassured us, rather than scare us away. I still get the impression that the market is more keen to ebooks than screencasts, but it would have been foolish to start without some form of market research.