(btw: Adium is my fave messaging app for Mac)
Well, a full transition away from email is still not complete, and maybe never will be, but since I've been at it all year, I thought I'd offer a bit of a break down on my experiences.
→ Efficiency: Emailing back-and-forth with students about a simple thing like assignment clarification can often take an entire weekend to settle up, with the first message sent on Friday, a response shot back on Saturday, and final clarifications wired back-and-forth on Sunday. By that time, everyone is exasperated. With IM, the student finds you online on Friday, sends you a query, and you deal with it on the spot.
→ More Chatty: IM seems to me to familiarize teacher-student interaction, something that tends to fit w/ my approach. Having a student find me on IM is like running into them in a hallway or the quad—we chat, catch up, settle a question or two, then move on. In this way, I like it and find I know my students a bit better through IM interaction.
→ Away Messages Have Pedagogical Potential: IM users have made a lot out of the away-message feature built into messaging software, leaving all kinds of notes, messages, and cryptic texts for users to find. Following suit but responding to different goals, I've started posting assignment updates and little notes to my students via my away messages and/or customized "available" messages. This doesn't guarantee that all students get the update, but since most of them seem to peruse away messages regularly, I'm guessing I'm getting through to many of them.
→ Spontaneity: I recently got an ecstatic message from a former student over IM when she got a teaching fellowship in her new grad program. I'm not sure that she would have written me a long email to express her excitement, but finding me on IM was easy enough and the techno-channel was conducive to her sending me a quick and exuberant message. I like this and receive lots of quick-and-interesting updates throughout the day.
→ Public/Private Problem: IM simply isn't an accepted pedagogical tool yet, so the first time I get messages from students they often write something like "Hey Professor, this is X, it's a little weird contacting you on AIM, but ..." This seems to be the biggest problem with communicating with students via IM right now, in that some seem to consider communicating with an instructor via this technology as an encroachment on the private. I say this in part because away messages can be, well, not the kind of thing students want their instructors to see, but also because the discourse conventions common to IM put students on a plane of familiarity with their instructors—and they may not feel comfortable occupying that plane. As a result, not all students have contacted me via IM, though I'm not sure the numbers are lower than typically reach me via email.
→ Contact Hours are Erratic: If I'm on IM and students have questions, they can message me and we can have a quick back-and-forth, but if I'm not online when they are looking for me, they're out of luck. Since I'm one of those people who spends 80% of my waking hours connected, it's not that much of a problem, but I'm guessing for those with non-jacked-in lives, this may pose a problem.
→ Composing Time Varies: I've noticed that some students seem to get uncomfortable communicating with me on IM, and as a result, tend to proofread and revise their loooong messages before sending them to me. On IM, this is downright unconventional, but since I'm their instructor, it makes sense. The downside of this is that I can spend a lot of time waiting for a response/turn to come across the wire.
→ Surveillance: The obvious problems with surveillance are kind of a no-brainer, but worth mentioning. With IM, students can see when I'm online and I can see when they are. This generally doesn't bother me, but it may spook you or your students out.
So those are my reactions to date. I generally dig using IM to chat with students and think it has many virtues ... particularly when blended with other communicative technologies, including that old thing called face-to-face. Did some of that today with some students, as a matter of fact, and my was it well worth it!