Last week an article in the New York Times decided to take up this vital question ("To: Professor@University.edu Subject: Why It's All About Me"), but the Chronicle of Higher Education has weighed in on the subject twice lately, too, once on IM in "The Professor as Instant Messenger" (registration required)and once a few months ago when it found that "some professors said they felt pressure from students to be even more responsive online" ("Professors Give Mixed Reviews of Internet's Educational Impact," 8/12/05). The responses on blogs have been interesting, too (example: thread at No Se Nada).
Disclosure: having had an e-mail address since 1989 or so when we chiseled out the letters on stone tablets and sent them via Bitnet, and being on IM for students for at least the past 5 years, I haven't seen this level of entitlement expressed by students. Ever. I have seen questions about grades, and a few years back a student would IM before class to snark obliquely about whatever s/he didn't like about the class, but the solution was simple: I turned off the IM client. The "24/7 professor" model could get to be a problem, as could demanding students, but are they really that demanding? When I can answer a question about an assignment in a 2-minute IM exchange, isn't it just easier to do so?
And why is the Chronicle (at least in its First Person columns) determined to feature only people who treat technology as if it had cooties, to use a fourth-grade analogy?