SEOmoz PS should really be called BS. Just right when I really started liking it, it becomes a per-membership and for what I hear the results are just as crappy as before.
I can understand why it was done, although maybe a donation link to help offset the cost of more resources to improve accuracy would have been viable instead of a monthly fee.
I have used that tool several times and for the most part it is pretty good. I think it has a way to go, before you would really want to count on it for a source of marketing.