[Apologies up front -- I am bouncing back and forth between two houses today and tomorrow, so if I appear more incoherent than usual, that's a convenient excuse, but Janet's nutshell of Berlin's taxonomy provides an opportunity to talk about computers and writing from a slightly different perspective.] 

First, a bit of context. I have major responsibility for designing and implementing computer environments for lots of disciplines (business, math, and English in physical classrooms, but the rest of the campus in open labs and online). When I talk with departments about what they want to happen in these online environments, my C & W background is invaluable. Sometimes they focus on the intellectual development of the student (learning through exploration). Other times they are interested in students getting a taste of the larger disciplinary community (the profession as it appears in web pages, for example). Sometimes (although rarely) they are interested in community building and easy interaction with students. I usually begin by asking why they are integrating technology into their courses, and the way I frame the question is by asking them what problem they are trying to solve. 

I had difficulty with this when I was teaching composition. The problems I devised for students were just that -- devised. As I work with other disciplines, I find the teachers have real instructional problems, and luckily for me, computer-mediated communication can often go a long way to addressing them. Obviously, these environments, whether they are classroom-based or exist more completely in the ether, help students reflect and learn, but the most important value I think they have introduced is the presence of a real audience, for online contributions on lists and in newsgroups, but more importantly on web pages. Students can find real audiences for what they write, in any discipline, and these audiences are not shy about responding to what they say. 

Composition theory can be a powerful base from which to understand the communication problems in other disciplines. 

I hope my comments bring in another thread to Janet's comments. Many of us are also involved (by design or necessity) in WAC; I am especially interested in how our base in computers and composition helps us in the broader context of college writing instruction.