Q1: Can anyone recommend some online book club/book discussion sites you are aware of, which ones you prefer, and why?

Q2: A related question is if you've leveraged some of the features built into popular e-reading apps/devices to contribute to online book discussion, and how that experience went? For instance, the ability to make Kindle annotations public and see the annotations of others could be a useful capability where, combined with a discussion forum, you could have detailed discussions about excerpts and passages from a book.


Background
In addition to the forums we have here on MR, I am looking to join an online book discussion group that is heavily moderated, allows for special-interest book discussion groups to form, and maybe one that has more advanced features (vs merely threaded BB discussions) to collaboratively comment and discuss ebooks. I might be willing to pay for a subscription-type service that offers these features, depending what they offer. Obviously some people are leveraging existing social platforms like Facebook, and basic support for this is built into some of our popular e-ink readers. Some are using the group discussion feature built into Goodreads, or similar sites. That sounds somewhat interesting as I'm already a member of Goodreads, but would like to hear from some who have tried it. Also it looks like there are some specialized book discussion platforms--one I ran across is "CommentPress"--that allow for advanced collaborative discussion and commenting directly with the text of an ebook.