An honest book reviewer should be unbiased regardless of whether the books were purchased or given. If the reviewer can not remain unbiased then they shouldn't be reviewing books. It doesn't bother me to disclose that the book was received for review, I think the big issue is whether the reviewer was PAID to review. The big crackdown is not really because of book bloggers, but due to the excess of review bloggers who are receiving cars, computers, tvs, cookware, and all the other big ticket items.
I assume anyways that a reviewer (regardless of the product) has been GIVEN the product to review.
I have a disclaimer at the end of my reviews. Pretty simple, really. I don't understand why every body is so upset about adding a sentence to their review.