I decided to join Goodreads in 2015, in part to see if I can get some good book recommendations from it, and in part because I really like to talk about books with folks so it seems like a network I'd like. That's my belated explanation why the Goodreads lists popped up in the sidebar recently.
Overall I'm still figuring out Goodreads. It is super-aggressive about wanting my Address Book which isn't going to happen. My rule is this: I'd be mad if a friend gave my email address to any social network so I shouldn't give out my friends email addresses. I think it's settled down a bit now, but the first few times I logged it that was like a "Here's the super-important next step!" and I definitely had to click "No" multiple times.
While rating a few books I discovered the latest Discworld novel, Raising Steam came out last November which I did not know. I'm reading that now so we can definitely put that down in the win column for Goodreads-as-recommendation-engine.
Anyway, as I said I didn't give up my contacts so if you're reading this and you have a Goodreads account ping me and I'll look you up. With only a tiny bit of judging on your reviews and ratings ;-)