Communicating with Students
As far as the issues raised by the discussion go, I think a lot depends on what sort of institution you attend. Burke raises the special position of professors at research institutions, though it should be noted that even most of those I know here at Wisconsin are open to if not always eager for e-mail communication from students. Even smaller institutions can vary greatly in the level of formality expected between students and faculty, with some institutions encouraging faculty to allow themselves to be called by their first names while others pride themselves on maintaining a more formal environment in which even students are customarily addressed by a polite title and surname. When there is face-to-face interaction, as with an office visit, expectations can be easily communicated through the terms of initial greeting, tone and body language, but sans that, entering freshmen in particular may simply default to the more familiar behavioral standards of the usually relaxed high school environment.
My own attitude is pretty student-friendly. To be honest, I like people, and enjoy getting to know the diverse array of people who pass through my classes, so some informality in tone doesn't bother me. I like to know that my students have a life outside the classroom and passions and priorities different from those of all my friends in academics. Even when tone in an e-mail slips into something demanding or something where it really should have been handled earlier, however, I think it's important to try and remember where students are coming from. Many faculty who stay removed from their students tend to underestimate the amount of stress students can feel under, especially during certain periods of the semester. This is not something I allow to affect expectations, but I try to be understanding and not make what I see as the root cause of a panicky plea for last-minute help or mercy on a grade worse.
I also noted Daniel Drezner's response, in which he called attention to the use of IM as a communication tool. I went to an undergraduate school where some professors gave out their home phone numbers for use under special circumstances. I hate telephones enough to shy away from that, but am now in my second course of giving out my IM screen name. Because I'm on IM almost all my waking hours, this definitely increases my availability, which is especially important this semester when I'm on the Beloit campus only twice a week. However, it does involve some sacrifice, as there are times when I might want to be available to friends, but not become involved in work, and any time a student IM's you it's going to be work-related. This has not yet become a problem, but I can see where it might be at some point in the future, and I still don't have a good plan for dealing with it, as IM's, unlike e-mail, seem to require an immediate reply.
Anyway, one other thing which crossed my mind - in this age of "helicopter parents," can professors expect to start eventually fielding e-mails from parents arguing on behalf of their kids? This has already happened to me once, and I suspect not for the last time.