I'm in that group as well, but it's more or less dead - a problem is that Goodreads doesn't really define what groups are about, and users don't really see in their "timeline" when something new happens in a group.
Maybe the mods of that group could have a monthly book club or so?
Edit: yes they do, and that's exactly what they're called, and there's already one for Hacker News: http://www.goodreads.com/group/show/94469-hackernews