The iBookstore is now live on the App Store (free) and comes with Winnie the Pooh and the ability to sample of any book in the store before buying. US-only and iPad-only for now, global editions are expected in the near future.
It isn’t certain if Apple will build versions of the iBookstore for Mac and iPhone/iPod touch like Amazon has built with the Kindle but it would certainly be welcome.
You can also drag free ePub books manually into iTunes as demoed here.
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