Very interesting. I've never used this feature. And I don't know, how is it supposed to work, when as Peter said quotas are account specific. Perhaps, it's created for only monitoring purposes?
Correct. The domain disk space is only for personal account management. It will message the owner of the domain upon over usage. It is not enforced at the system quota level.
If/when such quota functionality exists which allows quotas on a per-directory basis (instead of per-user), then we could look at implementing enforcement of the limit, but at this time, as mentioned above, quotas only work on a per-User account limit, so they cannot be enforced at the domain level.
In essence, it gives the User his own mini-hosting company within his own User account, allowing him to create domains in his account that he doesn't need to manage, but it doesn't give him the ability to let his "mini-clients" login to DA. They can have their own ftp accounts, which is all they really need to upload a website. Other things like creating email accounts, etc.. must be done through DA by the normal User, so it wouldn't be a feature-rich hosting company (unless he uses the API to let them do everything... ) .. but this is going onto somewhat of a tangent to the original question.