When van Dam gets to talking about hypertext in teaching, I really perked up. He thought then that "we are about to go over the knee of the exponential curve," citing HyperCard's popularity and emerging systems like Xerox's NoteCards and Owl's Guide. Of course none of these remain in wide use, especially in teaching, and hypertext remains of primary use in the classroom as a reference rather than as an authoring, working, or collaborative tool. I feel like we're still just short of the knee of the curve.
Individuals are pioneering use in the classroom. Others are disseminating potentially rich tools which achieve "user friendliness" by emulating non-digital systems... and which then don't push the envelope much. Others are using hypertext extensively, but in courses that are at least partly about the medium.
I'm waxing morose, here: educators may have gone over the knee of the exponential curve in our reading and research, but not in our writing or working.