Given they have quality relevant content about the subject of course. What about question sites like yahoo/wiki answers?
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Long tail searches or "unpopular" subjects as you've stated have a better chance of ranking well. It all depends on the search query.
Popularity of the subject is one of many factors that play into rankings. I +1 this. This is why I rarely see hubs
Quality content can rank well :) but, as Farmer Rachel wrote, subject popularity plays a role. I search for things related to programing - this is why I don't see many hubs. I see forums and answer type sites. Both hubs and forums can rank well :)