Trubeck describes the desired goal of writing technologies as "cognitive automaticity," the ability to transmit ideas wholly formed from our brain to the page, so that we don't forget our poems about Kublai Khan's pleasure domes and so forth. But I'm not sure that's always the case.
How often do we have such gold that it /must/ be put onto the page as imagined? Certainly, in the case of dictation and stenography, we have the advantage of operating on the level of spoken rhetoric, with all the directness, engagement, and potential loss of focus that implies-- which makes the dictated nature of works from Paradise Lost to Dialectics of Enlightenment doubly impressive. In fact, I think that students should do more dictating and speechifying. We have the technology for it, and (as in the case of Trubeck's son) it could be helpful for writers with certain mental blocks.
But oftentimes, we need to work over pieces. Slower forms of writing lead to more simultaneous reading. The processing lag of handwriting leads us to analyze and reinterpret our work as we create it, and may take us in unexpected directions. While that might seemingly make our internal editor stronger, hard copy writing is also harder to delete; its physical reslience makes it harder to give into self-doubt and take it all away at the stroke of a key. It's also easier to give up on a digital document and hit print or send. In my first year of university I often forced myself into drafting by writing on notepads before transcribing it onto computer. The act of typing up a paper forced me to re-read the text and re-evaluate it.
I might seem a willing hypocrite, having typed this up on my netbook, but I'm not arguing for slow writing exclusively--there were certainly times in university where I had 6 hours to turn long-stewing thoughts into a paper, and I thanked great Theuth for this invention. What I am arguing for is a greater diversity of writing practice. If you get too stuck into one method, its negative consequences build up like mercury in a fish. So let a thousand prose flowers bloom. It's important to periodically rewire your brain, anyway.
[and no, I haven't yet read all the online responses. Give me a break, I'm catching up as fast as I can.]