Goodreads is desperately in need of a strong competitor.
replies(4):
Not needing to start from scratch would make building a competing service a lot easier. Sites like Stackoverflow have reasonably open licenses on user data, so you could theoretically use that data and build an alternative if the site fell apart. I'm guessing that's not the case for Goodreads though, at least for things like reviews.
But even pulling in basic category information would be easier than starting from scratch.