In a word -- none, at least that I know of. But I also don't know of any studies on the pedagogical effectiveness of using overhead projectors. I do think it would be interesting to have some case studies, but that's a bit out of my field and I'm also not convinced it's worth a great deal of effort. Why? Because the Web is fast becoming as ubiquitous as overhead projectors. I recently heard a colleague at a conference mention that he had a few years ago embarked on a study to see if using word processors improved students' writing or whether the same quality of writing was coming from students using pen and paper. He never finished the study because he realized it was pointless -- students were going to use word processing regardless.

I believe use of the Web -- or of the next generation of networked information servers -- will soon become so commonplace that such studies will quickly become irrelevant. What we do have to ask, however, is how to use this tool, this medium in as effective a way as possible. There is where I would like to see some studies undertaken. One probable conclusion -- responsive learning through interactive Web pages is more effective than passive Web browsing of static pages.