Ask HN: Review our startup (iPad app enabling communities within books)

We have some experience building web apps, but this is our first iPad application. We hired a freelance developer for the software development and did the design ourselves. We're obviously just getting started and there's a lot of room for improvement. We launched today and we're already getting a lot of helpful feedback from users, but I'd also be really interested in hearing feedback from an entrepreneur's and developer's perspective. You can download the app here to try out: http://openmargin.com/ No need to sugarcoat the feedback. The more critical the better.