* The green on black is very harsh to my eyes. Have you considered alternate color schemes?
* Add social network profile availability to the results. This isn't something that other domain name search services offer, and could attract people wanting to know if their startup name is available on Twitter, Facebook, etc.
* Add search traffic from the Google Adwords API for my favorited search terms.
One bit of feedback: It does not indicate if the base search term is a free domain on it's own. I understand that is not the common case, but it does mean a user needs to check that as well, outside your search.
Isn't "the number of users buying a domain" the best metrics or at least "the number of outgoing clicks to the registrars" ?
Affiliate revenue is a one metric, but I'm not sure that completely reflects the quality either. I'm not sure it's possible to look at one metric and get the full picture.
The trick is fitting all those logos in there while still keeping the dialog a manageable size and designed well.