Just to make sure, I checked Overdrive Media Console quickly, from what I can understand, you can't actually import your own books? You can rent or buy from their store or affiliated library but you can't bring external content... I checked the desktop app and can't find a way to load epub files into the console...
Thanks
The PlayBook app says that it can display external DRM free epub books and documents. It has a directory for downloads, so a desktop app/manager is probably used somehow. I don't have that, but use Book Reader for the DRM free epubs.
