TRickFletcher
I have many more than 20 videos made - but I find my students use them more frequently when they are created to coach them through specific problems. They use them as often as they visit me in office hours. I've also just completed a series of 35 videos for a textbook publisher that walk first year college students through very difficult chemistry problems that use multiple concepts. These are not short single topic videos so we will see how useful they are in practice. They are meant to help a chemistry student learn to think like a chemist and the jury is out as to whether that can be taught by video.
I would be happy to talk about helping with your effort in science, specifically in chemistry. I am sure there is much to be done and surprisingly, not that many working to create more content using this medium. A mix that can also provide real-time Q & A is particularly interesting. I can be reached at fletcher at uidaho dot edu. Here is an example of the kind of vid that students use to help them solve a specific problem: http://www.youtube.com/watch?v=49k88Alfh88