Apple introduced an update to iBooks 3.0 very recently and has already pushed out an incremental update. The update resolves an issue where iBooks may unexpectedly quit.
The new 3.0 update introduced several upgraded features including:
Introducing iBooks 3
• See all your iBookstore purchases in iCloud—right on your bookshelf with iOS 6
• Scroll vertically through your books with the flick of a finger using the new Scroll theme
• Receive free updates to purchased books—including new chapters, corrections, and other improvements
• Look up definitions for words in German, Spanish, French, Japanese and Simplified Chinese with iOS 6
• Share quotes or thoughts about your favorite book with friends on Facebook, Twitter, Messages, or Mail
You can read more about iBooks here.