I recently was contacted by a client to help clean up their web properties. It appears they have one main site and a bunch of little other domains based around that main one. The little ones display specific information of the larger site and pull that specific info to display. But the links created all go back to the main site. It's been like this for several years so I am guessing it's not hurting their search results. Or has it been and it's just not apparent? These seem like they would fit the bill perfectly as a defined mirror/door site but I wanted to make sure I had my facts straight.