Although it's a rather small social media platform, GoodReads is my favorite. It works well, because you can link it to Facebook, Twitter or both.
It's all about books. You list the books you read and you review them. That's it!You can recommend them to each other, and study your friends' reviews. For book lovers, like me, it is an excellent tool and great fun. As book author, it is also interesting to see what my books are doing. And as a Kindle user, I can deliver my reviews directly from my Kindle. What's not to like?