Comment 13 for bug 453169

user-group rights should not be a problem:

1. if you run rsync as an unprivileged user, you should not be backing up other people's files
2. If you are backing up data for several users, then your rsync should be running as root... in which case your rsync will be able to manipulate user/group settings.

The real problem is, of course, when you try to use some brain-dead filesystem which doesn't support users and groups. I really think that it's better not to support those filesystems than to give up rsync over ssh.