The latest revision covers new Mule 3.5 features including new OAuth functionality and data synchronization. There is also a new chapter on orchestration - something that the original was missing for people new to Mule.
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Good news is that if you already purchased the ebook edition then these updates are free and you can grab the new edition from O'Reilly.
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If you would like to review the book on Amazon, O'Reilly or Google books let me know and I can send you a free review copy.
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Buy it direct from O'Reilly and get free updates for the lifetime of the book: http://oreil.ly/mule-cloud