Skip the post Ethics in Book Reviewing Survey: The Results at Critical Mass and go directly to the Comments section for a spirited discussion of reviewing (or, rather, the lack of reviewing of) self-published books.
In particular, look for the paragraph ending with the term "gang-reviewing." I do think she made an interesting point there. A little further down, another commenter talked about the assumption "that the few hundred literary agents and mainstream publishers who decide mainstream publication ALWAYS know best, and will publish everything worthy of going into print." I'm not passing any judgment on that one. I just wanted to throw it out there for inspection.