If you upgrade to iOS 7 be aware that when existing OverDrive Media Console (OMC) app users upgrade to iOS 7, the app will fail when trying to open a DRM-protected eBook. New or first time users of OMC are unaffected by this issue.
OverDrive is resolving the issue but in the meantime, here are immediate remedies for users:
1) Re-authenticate the app with your existing or a new Adobe ID.
2) Uninstall and re-install OMC which will also require you to re-authorize with Adobe. IMPORTANT NOTE: A re-install will clear a user's bookshelf, history, and app settings.
Audiobook users won't notice that anything is different unless they attempt to download parts of audiobooks they already downloaded to OMC before upgrading to iOS 7. A user will receive an error message informing them to download the title again.