Apple released iBooks 3.1.1 for the iPhone, iPad, and iPod touch on Wednesday with slim notes saying it improved compatibility with iCloud and iOS. iBooks is Apple's ebook reader app that's currently available only on iOS devices, but will be part of OS X Mavericks when it ships this fall.
iBooks for iOS gets improved iCloud support
With only the vague iCloud compatibility note to go on, it's likely the update addressed syncing issues for bookmarks and notes, and helps lay the ground work for iBooks in iOS 7, which will be available in the coming weeks. What we haven't seen yet is any interface changes that do away with the app's skeuomorphic elements in favor of the flat look that's part of iOS 7.
iBooks is free and is available at Apple's iTunes-based App Store.