I think anything can and should be criticized, even Carrara on the Carrara forum, as long as the criticism is objective. If you lose objectivity then don't bother posting since you really don't have a point. But if you do have a point, we all benefit form your critical post. We can't just stick our heads in the sand and not realize that something is not good or could be improved. Objectivity is the key.
I for one would like to hear what Petshoo has to say. Specially since I have not upgraded. I would also like to hear from old Carrara users telling me just how much better and speedier C4P is. I stress again, as long as the rant or criticisms are objective, it makes them valid. At least thats how I see it.