[jonathanwallace]

There's subreddits such as http://www.reddit.com/r/books and specific subreddits for genres such as http://www.reddit.com/r/SF_Book_Club/ amongst others.

You may also find discussions on reviews on http://www.goodreads.com/.

[bobcostas55]

/r/books with its 3 million subscribers is really, really bad.

/r/literature is much smaller and therefore better. Way more interesting content, but still extremely entry-level though. And plagued with stereotypical redditisms (one of the top posts right now is Tao Lin translated to Latin).

[redacted]

Try looking for small genre-specific subreddits, like /r/printSF for science fiction books etc. More focused and insightful discussion seems strongly inversely correlated with subreddit size.

[Apocryphon]

I'd be interested to know what the public consensus on Tao Lin is.