The app has been updated with a more iOS7 look and feel with a Newsstand-like frosted glass background in place of the library shelves. The iBooks store has also gotten a makeover, and it now looks like iTunes. The page curl
and faux two page crease still remain, however.
Update: This version of iBooks requires iOS7.
I for one am pleased to see the change; I've never understood why Apple thought that users would be more comfortable with the fake bookshelf than with icons.