It's different in a few ways: it's a web-based system that uses hashtags to guide the conversation (which can be shared out to Twitter and link back into the book). Each ReadUp/bookgroup created expires in two weeks (so it's a limited-time "event"). It also has real-time messaging, so you can send a short note to someone else reading the book at the same time, or message everyone in your group, to have them go to a different section.
Here's some more detail from the actual app:
Use this app to create a ReadUp from a selection of Harper Collins titles, to "meet up" inside the book. Share notes with friends paragraph by paragraph, leave comments for the author, message others inside the book as you read, or host discussions. Just choose one of the samples listed here, then share the link to invite people via email or Twitter. They can get to it at that link until time runs out. All Harper Collins ReadUps disappear after 14 days.
This project is a mashup of two services: the Harper Collins Open Book API and the ReadSocial API. It could potentially display new books daily, weekly, or monthly. ReadUps is built for the browser and optimized for iPad and laptop environments.