http://crookedtimber.org/2010/12/12/how-should-students-to-address-professors/comment-page-1/#comment-341754 - an interesting dicussion: should students call me Dr X (esp odd, my surname not being 'X') and I call them by their surname: 'Oi Smith, what is meant by synthetic a priori? eh?'
Or maybe not.
I am kind of used to 'You' and 'Dave' - but the comments via the link really vary: let me quote a couple:
Maybe I’m just cripplingly old-fashioned, but I cringe when I see some of my colleagues insist on having their undergraduate students call them by their first names.
I find anything other than first-name address really awkward, but I think British students tend to gravitate to this as the norm anyway. American visitors on JYA programs tend to be more formal, and even sometimes address me as “sir”, which feels very weird indeed
(our visiting American [BCA] students sometimes do this - I rather like the implication of respect - but they soon learn....]
I’m struck by the number saying they use last name only (if I read it right). In direct address, I find that exceptionally rude, unless the person using it is so close to me that I can take it as jocular. The only situation where I regard it as normal is among school-age boys.
Not sure it ever really feels awkward these days? If I refer to a colleague in a class - I am sure I use their first name. As in: don't ask me, but am sure Roy will know.....