Am Sonntag, 13. Januar 2013 schrieb Ludovic Courtès:
> >> If --build-users-group is not given explicitly, check for the group
> >> nixbld and use it if it exists.
> I’m not sure if we want to automatically use a given group name.  What
> if that name was used for something else on this machine?  Granted, it’s
> unlikely, but it’s not completely impossible either.

In that case, the user would have to give the builder group explicitly 
anyway. I think that using the guix-builder group as a default should be a 
very safe bet.

Andreas