Don't get me wrong – book reviews often offer telling insights about the reviewer as well as, hopefully, the book under consideration. They are often fun to read, if only for the small jabs that reviewers make when the (dubious) benefits of anonymity are removed. My favorite is: “The text had minimal typographical errors.”
Writing book reviews can be, as Ana Dinescu notes , an interesting and worthwhile undertaking. Reviewing can help you organize your thoughts while contributing to the refinement of scholarship more broadly. However, for the un-tenured or otherwise vulnerable among us (including graduate students like myself), writing book reviews can be a daunting and inhibiting task.
IF – and, as a prolific reviewer, I use the word deliberately – one were to encounter a promising book title (see @AcademicTitles), one might excitedly request the book from a journal. Upon receiving said book for review, you could potentially determine that your moral compass in no way allows you to write a positive review of the content. What would one (say, one graduate student like myself) do in this scenario?
One may, if one were the quitting sort, return the book to the journal with a note stating an inability to complete the review for various reasons.
Or one may, if one were the intrepid sort, press on and review it anyway.
Should one choose to press on, one must strike a balance between flattery and critique. It is best not be be disingenuous with either and careful with both. No one should publish a review that is all sunshine, lollipops, and rainbows, but you shouldn't go around making enemies through your snide commentary before you've made a name for yourself in Ye Olde Ivory Tower. Otherwise, you'll have a name for yourself. They will call you That Uppity, Rude Reviewer, which will not bode well when you come up for your own review by hiring committees or other assorted gatekeepers.
Because one's future may potentially be at stake, I find writing book reviews early in one's career to be a process laden with political baggage. However, it is also a useful exercise in diplomacy.
Based on the advice I've gotten from others, the compliment sandwich model seems to be a prudent approach to any book review. As is the case when reviewing student papers, there's usually something positive to be said about a piece, there's always something to critique, and it's best to conclude with a bit of applause or encouragement. Book reviews that are worth reading find the balance between reasonable compliments and responsible critiques.
Writing your own book, on the other hand, is the way to get all your jabs in. Where else can you call someone “an amateur and unreliable ethnographer” or dismissively refer to a prestigious scholar as an “undergraduate”? (Other than the blogosphere, that is.)
Happy reading, and good luck writing!
Amanda Murphy is a doctoral student in the School of Canadian Studies at Carleton University in Ottawa, Canada. She makes academic-y cartoons at murphyaoink.blogspot.com  and blogs at dessertating.wordpress.com . Readers can contact her at email@example.com.