I'm trying to upgrade from version beta 17 to beta 18 with no success. After mounting the dmg, dragging Stanza to Applications shows a dialog box asking if I want to replace the current item. If I answer "yes" a Copy error is displayed telling me that I don't have permissions to access to some items.
I didn't find any report like this here, so it must be an unknown bug or, most probably, something with my Mac. I don't have any problems upgrading other applications.
My Mac is a unibody MacBook, SnowLeopard 10.6.1, and just a few books under Stanza library. I also have Stanza iPhone.