If you work in technology and are considering working in Health IT [in the USA], you should read this book. It is a good guide to many of the challenges in Health IT, with chapters on how clinics and hospitals use information, HIPAA, interoperability (e.g., HL7), ontologies (e.g., SNOMED), why paper is still very useful for many kinds of records, billing, Meaningful Use, EMRs, etc.
There are some appropriately negative reviews at O'Reilly and at Amazon, mostly regarded the editing and some places that are obviously rushed.
I would also note that this book desperately needs an index and, for each chapter, a list of further reading and tips on how to stay up to date -- a list of major blogs and/or Twitter feeds for each area.
One last thing:
There is another reader who might check out this book: The everyday citizen. Even though the vocabulary here is technical, there are many asides regarding why the USA has such expensive IT for healthcare. Our Health IT is absurd, but there are historical and economic reasons. It is hard to imagine someone who has read this book and still thinks that healthcare in the USA can be cheaper or more efficient in its current economic situation.