The most effective training videos combine onscreen demonstrations a la Camtasia with audio narration that explains what's going on and also points out tips and pitfalls. Some vendors provide DVD videos that play back on any DVD player - which I prefer - while some use MS codecs that will only play back on a PC.
For content I would like a primer that covers the basics and focuses on efficiently doing everyday tasks. For example, I don't bother to use frames but I probably should; I just don't fully appreciate the benefits over using multiple pages.
I would really like to see basic and advanced scripting explained and demonstrated. I've printed out the manual from Opus but find the cross-referencing confusing and frequently lacking.
It's my opinion that the best training is project-oriented. Devise a project that incorporates all the elements you want to discuss and then methodically demonstrate all the actions and logic required to build the finished product. Anticipate the viewers' questions and answer them. Put them on a DVD with a front-end that allows non-linear lesson access, of course!
Then send me the bill.
Walter