I just checked and this is indeed the case. This request can be 
closed/rejected.

If I say "identity" I really mean the identities from the Horde prefs, 
not the "own contact" from Turba.

This does work, but only if there is an entry in Turba marked as the 
users own identity. The problem I had back then, was that new users 
frequently forget to mark an identity as their own (as far as I can 
see there is no way to force them to do so).

I have worked around this by setting up the users account for them 
(including this step), but occasionally they manage to remove their 
own contact information and the problem surfaces again.

There is no need to create a hook. The admin just has to set the 
default location and it's part of each user's identity, which is 
already checked in _findLocation().

Add another method of trying to figure out the location, just before 
falling back to GeoIP location. It might be possible to do this via a 
hook as well, but by doing this automatically could save system 
administrators the effort of having to write a hook themselves.