DRM-free ebooks work with this app as they do with the PC version. I just downloaded and opened a DRM-free mobipocket file from here: http://www.feedbooks.com/b

DRM-free ebooks work with this app as they do with the PC version. I just downloaded and opened a DRM-free mobipocket file from here: http://www.feedbooks.com/book/88 http://www.feedbooks.com/book/88, so the problem seems to be specific to your O'Reilly ebook/Mac app install.