Some children respond better when they know other children are going to read and respond to a book, which is why book discussion groups are great. I also think parents should be required to read what their children read at all ages so they can really connect with their child and be able to answer questions and instigate discussion. This is one of the reasons parent/child book groups are so great.
We also regularly hold online chats with authors of books on our summer reading list, which kids can join from anywhere they can get online. Kids get really excited to ask the authors questions and just talk to a 'real live' writer. We have a regular chat-room just for children to talk about the books that they've read, which is catching on.