social network book clubs

Hello all,

Reaching out for your wisdom and experiences. I'm teaching summer school and have been able to engage students typically rather disengaged from school using a Ning site for the book we're reading. The students are supposed to complete profiles and answer questions, blog as a particular character. Its all working fine and good, and I'm trying to figure up how to scale it up for the regular school year when I don't have students all reading the same book. Has anyone used Ning (or another site) to create an online book world where students track what they've read, write review, make recommendations, etc.

I found a site called http://www.shelfari.com -- but I was hoping for something a bit more closed (our students and teachers only)

Any thoughts?