2.0 is much nicer. There was a bug in the 1.8 beta that's still there. If I control/right click anywhere, in the library or after highlighting some text in a book, I get a beachball that seems to say. On 10.8.2.
It seems also that any dialog that says don't show this message again doesn't retain the setting between restarts.
For what's to come, a search field to find books would help a lot. After adding hundreds, how do you find 'em? Maybe you'd consider editing metadata, something like highlight one or a few books, command-I and Get Info, like iTunes. If I want to edit a title, author, or publisher, it's quite a pain otherwise. Even without that, perhaps, when opening a document, you can re-read the metadata? Like if I add a missing publisher, I need to delete and re-add to the document for it to be shown.