http://online.wsj.com/public/article_print/SB118729653805300071.html There's an entire article in the Wall Street Journal about how they gained so much popularity by buying blog posts. Hmmm, I wonder if Google will stick it to em? If they don't (which I hope nothing happens to them), then Google will have a precedent of not punishing a site for buying links. Future lawsuit material for websites that are punished by Google (why did Apogee not get punished and we did? - kinds of lawsuits).
I think the issue is with buying links blatantly to manipulate Google's algo. That is, buying from people who sell links based on PR. I don't see any issue with paying people to write about your site. It's only natural they include your link in a review.
I agree! Andy Beard had some interesting thoughts on this as well. He said they're paying for his time to review or post, not for the link.