I periodically rate books that I've read on Amazon and then look for recommendations. Unfortunately, 95% of what I get recommended to me are books that I've either already read or have considered reading and decided not to read (no matter how often this and similar rec systems tell me I might like Neal Stephensen, I don't). I'd love to find a system for rating books that was superior, but it seems like it would be quite challenging. A smarter system for books is desperately needed.

OTOH, I've been told that Pandora has gotten considerably better over the last two years and that a well-tuned Pandora station can often deliver significant amounts of music that fits your taste and that you haven't previously heard of. Of course, tuning a station takes a fair bit of initial effort.