Well, our in-class IM-ing proved to be as de-centered as a conversation can get, I think. I was in the group led by Jim. It took us a while to get everyone logged on, etc., but once we did, I'd say we had a few "productive" discussion threads, as short as they may have been.
I found myself listening to Kristin's voice above others in that group, mainly because I was looking for a guide/someone to take control. As it turns out, Kristin was trying her hardest NOT to be in control. Still, I initially felt this responsibility to "accomplish something" in the look-we-are-being-academic sense of the phrase. Then, after the de-centering really took effect and all the jokes and emoticons were flying from every direction, I decided to stop forcing the issue and start joining the fun. And what fun it was... especially after we all joined forces and had a fiesta de chaos. Let loose, laugh, and know that as grad students, we'll surely find a way to analyze this in the language "academese" on Tuesday. It's in our blood to do so. :)
In classrooms of my own, I think I'd use IM-ing, but rather than let my students go wild, I'd hand them a few prompts that they would need to address as part of the activity. Then, as long as they cover those questions (even if it's minimal coverage), they can have as many emoticon wars and unrelated madness as they like.