This is a great idea and one I've tried in the past.
The following forums are on longer accessible via menu/links, but I've placed the links below so you can see what was tried in the past. I stopped them due to lack of interest, but I think members didn't really know they existed. We have more traffic now so they may do better next time. Anyway, it's on my rather large todo list to revive this or something similar.
Books For In-Depth Discussion - Discussion threads on books
Study Hall - The idea here was to sponsor a book every month that would be read and discussed as a group, similar to the monthly theme I've started.
Check these out and let me know what you think. I'll bring one or both of these features back if there's enough interest.