On Thu, Apr 24, 2008 at 2:36 PM, Philip Newton <[log in to unmask]> wrote:
>  I would address someone as "du" when:

Keith mentioned online -- using "du" is fairly common in German
Internet communications such as Usenet; the Wikipedia article says
that this probably stems from the fact that certain "in-groups" would
tend to use "du" amongst themselves and initially computing was open
only to a certain kind of technical-minded person, so users of
communication networks felt a bit as if they belonged to a common
group and could use "du" freely.

At any rate, I've noticed that people on German Usenet will tend to
use "du" even if they've never met their addressee before nor been
offered the "du".

I'm not sure whether this extends to online forums.

As for email, things tend to be slightly less formal than in
face-to-face communication or paper mail, but I'd still use "Sie" in
business emails. (But I'd often start them with "Hallo Herr Müller,
Sie haben ..." rather than with "Sehr geehrter Herr Müller! Sie haben
..." as in a letter.)

Philip Newton <[log in to unmask]>