I am a member of a few groups on the social media site, Linkedin.com. Recently, a member of the group called "Project Manager Community" asked the following question : "Does having a PMP state you're a better PM compared to one that doesn't have this certification?".
So far, there are more than 110 comments and they are still continuing to be added.
My answer was to comment that it is not just the qualification, but that it must be combined with experience to make a good PM. The depth of knowledge that the PMP exam makes each candidate understand is far superior than any other PM exam that I have seen, or indeed taken. Each candidate must know the PMBoK inside out and understand the complexities and dependencies of project management.