Just a thought, can we get enough information to make decent decisions about long tail items in a hyper-niche information market? If you anticipate a power law distribution, most stuff won't be rated, linked to, or written about enough to decently feed a recommendation engine. Does it even matter? If stuff is cheap enough, I just need to get in the vicinity of items that might be attractive to and then I can root around to pick something. A few clunkers doesn't really matter as long as I get a steady stream of useful things, and a few hits.
Maybe the best long tail tools will help people window shop. Instead of trying to make recommendations, make the overall process of sifting enjoyable, efficient, and social.