I agree. I'm not sure what the shelf is intended to be. I shelved all the works in progress I'm currently reading, assuming it would make it easier for me to find them to review on my home-page, but that doesn't seem to happen. I also notice that the only shelved books that appear on the crawl are published books available on Amazon, many not workshopped on the site.
I guess it's just a free-for-all at the moment and it means different things to different people. I probably won't bother using it anymore, frankly.