It should go without saying, but for the record: TUAW isn't involved in this practice, and never has been. We will use promo codes for reviews rather than buying the apps directly, but a promo code doesn't guarantee a review and it definitely doesn't influence our stated opinions on the products we cover. Informally, our editorial team gives a thumbs up to the OATS standard, although TUAW hasn't officially joined the sites promoting the 'code of conduct' for app reviews.
Nevertheless, this is an interesting issue. My main question actually revolves around whether or not this practice actually "works" for the developer -- do devs who pay the $25, or whatever these "Reviews R Us" sites are charging, actually see returns in their product's sales or downloads?