I find Goodreads recommendations to be stale. I have ~200 books in my account, all with my personal ratings, but I never seem to get any new recommendations from Goodreads as I add new books. The recommendations I do get are usually just mainstream bestsellers too.

I was thinking that with all the data Amazon has about folks (very detailed reading habits from Kindles, for example), they could find people with similar interests to me and recommend the books that those people liked most but that I haven't yet read.