At my sons school (boys only) the boys only call each other by their surnames, first names are hardly ever used. It's not seen as rude in this little corner of England.
I went to boarding school very close to where you are Neil, and we too only called each other by surname. But that's just it, it's schoolboy, its impersonal and has a connotation. Wouldn't dream of doing it now, even to those same friends; not unless I was being cheeky or condescending or in jest.
I can understand maybe our friends over the pond do it differently; like so many other things.
