I like reviews, but biased one's are a strict no no. I think Rich meant about biased reviews when he said reviews.
What I think is as long as the review is unbiased and comes from an user who has been using the reviewed product should be allowed.
However hardly any user who has spent $$ on a software is going to say the negative about the same, the world is highly reluctant to admit purchasing (and choosing girlfriend?) mistakes, they would rather kill themselves