Not surprised. Goodreads is for books what IMDB is for movies (which Amazon also owns). It'll nicely complement Amazon as a recommendation engine to push buyers to amazon to purchase books (which it already does). I use goodreads to track books that I want to read at some later point; and have used it to discover new books.
Atleast I'm glad it was Amazon vs "Any Other Big Corp" because I believe that Amazon will keep the service alive vs shutting it down or trying to absorb it somehow.