Would prefer namespacing type of implementation so it would reflect also the clone urls. More than one level should be possible. This would help Enterprise usage. hgweb already does this (I guess bitbucket does it with one level username namespaces).
I decided to not implement this.
Having repos groups it's easy to do a symlink to some other location and make group out of it.
It's to much work to handle conflicts and manage multiple locations. I don't think it's such a big limitation for rhodecode not having this.