No, not all my reviews are positive, but it has been a while since I have posted even a lukewarm review. That is intentional. I got tired of making half-hearted recommendations for things I wasn’t thrilled about. Especially over the last two years, I have become more and more picky about what I am willing to recommend. So, as a result, all my reviews are pretty positive. If I don’t mention a book that I have been asked to review, I either haven’t read it, or I’m not willing to recommend it strongly.
EDIT, 23 Nov. 2013: Over the last year since this post was written, I have chosen not to publicly review several books. However, I have contacted the publishers directly in those instances where the book was sent to me as a review copy and have submitted my lukewarm or worse comments directly to them, in the hopes of both sparing them public shame and of improving a second edition, should one be created. I thought that was worth sharing.