As I have noted, several people in the current debate about blog reviewing have stated that they write only positive reviews, as there is too much castigation in the world already, and that if they don't like a book they don't mention it. However, as a writer I feel very strongly that a bad review of my work is far better than nothing at all. A bad review at least lets people know about a book and gives them the chance to make up their own minds, whereas not to be mentioned is in effect to be silenced, the worst fate a writer can face.
Much has been made by both Sutherland and bloggers of the need to be able to 'trust' a reviewer's opinion, but I find this stance pretty suspect, if not elitist. One should never assume that a reader will 'trust' your opinion as a reviewer; in my opinion one should always review with the acknowledgement that one could be wrong. As a reader too, I feel the same: I want to be given the chance to make up my own mind, and I can't if a book is never even mentioned (and I don't happen to know about it). What's most important is the airing of opinions - debate, discussion. In my reading group people often change their minds about a book after an evening's discussion, or even about the question of what books are for. (For an example of this see our latest discussion.)