Just stumbled across Marvin in the app store after getting fed up with iBooks and I have to say that I am really impressed with what you've done so far. I'll post with more detailed feedback and some suggestions when I get home, but I did want to report a bug I am facing (which may have already been brought to your attention).
After I build a Summary and try to add it to my Library, it always gives me an "OOPS, There has been an error adding the summary to your library" error. The result being that I can never read any of the summaries that are created. Not sure if others have reported this, but it happens to me every single time. I'm on IOS 5.0.1, Jailbroken, on the iPad 2. Thanks a ton for all your efforts and I'm looking forward to the next update!