I think Stephen Draper has really brought a key issue into the spotlight. Much of the teaching/learning that is done through the use of a CAL systems rests entirely on the shoulders of the user. The number of possible variations that the CAL design would have to be able to account for are almost endless.
Educators respond and adapt as necessary in the classroom or lecture hall all the time. For a computer system to do that would require an AI, constant control by a human educator, or some really insightful designing. I think we might even need to ask if we really need to replace the human and whether a better strategy might be to extend the abilities of the human educator?
Stephen's point about the implementation of e-mail is well taken. Really it is just like any other learning situation. If you put a group of students together and say "discuss" they will eventually reach a purely social level. For e-mail to remain an active academic forum, the students/learners need to have some kind of direction. It's no good to be given a soap box to stand on and have nothing to say. This listserv is a prime example of a good way for e-mail to be implemented. The e-mail can be used to extend the learning environment beyond physical and time constraints.