Hugh Schwyzer notes a correlation between the number of students e-mailing their professors and the number of students actually coming to their professors' office hours. I'd have to agree. My own office hours are generally populated by myself; some semesters go by without a single student visitor. There are ways of remedying the absence of student presence, of course; I require one-on-one conferences with all of my students in freshman comp, for example.
Of course, this becomes rather frustrating when students claim on their evaluations that I'm "not available," even though they've never shown up in my office!