I've gotten several requests for new forums. A few have been esoteric topics and others have been mainstream (like Infoseek). The trigger we look for at this point is atleast 10 unique posts for a subject before a forum is created for it. I'm sure you realize we don't want 'dead weight' forums that never see any activity. With 10 posts already created, then there is there is a need for such a forum. We look for posts of this nature, in the Webmaster World general board, in Search Engine Promotion, and to a degree in rc's Foo subboard. By using those general purpose boards as incubators, we stand a pretty good chance of finding the quality topics from the noise.
