Quoting Robert Williams:
> I'm facing the prospect of creating hundreds of users and then
> specifying their permissions. Does anyone know of a script or other
> tool to help automate this? Or should I start rolling my own?

If I was you, I'd use Perl and create your own script. Take a look at
editusers.cgi and look for $action eq 'update' for adding to groups.

#!/usr/bin/perl -wT
use Bugzilla;
use Bugzilla::User;

my $user = Bugzilla::User->create({
login_name => 'user.email@there.com',
realname => 'User',
cryptpassword => 'P@$$w0rd');