John Gruber recently discussed some recently re-learned lessons about immediate feedback in text chats. It seems that Google Wave repeats a mistake made by iChat 1.0 wherein text appears immediately on the remote end as the user types it (anyone remember talk(1) ?). As it turns out, many people don't like people to see their messages as they are composing them. It's like letting everyone see your thoughts as you refine them. But then Gruber observes:

I never mind instant updating when I use SubEthaEdit to collaboratively edit a text file, but I can’t think of a good reason Google Wave uses it other than the demo factor.

But this makes perfect sense — we use chat tools and collaborative editors for entirely different purposes. In chat, the goal is communication, to clearly express one idea to another person. With SubEthaEdit, the goal is not communication but to collaboratively create something. In this case, the thought process is important to the user's task — it's the very point of collaboration. When we work together on an artifact (whether it's a report or code or something entirely different), we benefit from our own half-baked ideas and seeing the half-baked ideas of our partner. It's expected from the context. But in chat, we feel the need to present our own refined ideas, even if informally.