Perfect, just what I was looking for.
This is a wheel that doesn't need to be re-invented, especially when there's a nice, round, very usable wheel like this ready to bolt on :)
This module is simple and does its one task exceptionally well. The interface is simple and easy to use. And best of all I was able to replace a whole boatload of ugly regex with is_domain($domain). Can't ask for more than that.