I approached a reviewer this morning to ask advice on asking for a review. He said most review sites have the terms listed (and check for bloggers, some of them are incredibly well subscribed to) and that a polite advance can do no harm - other than a no. But approaching agressively or sales-pitch-y like won't get too far, I think. We need reviews more than they need dime a dozen debuts and self-publishers, after all. So, I think a polite enquiry will do no harm. But then I think being polite and friendly generally nets more profits than shouting my wares from a rooftop. And it's infinitely more relaxing...