I have been seeing more and more searches for this as of late and being that there is so much bad or incomplete information out there when searching for this I figured I would give everyone a thorough answer.

Let's take a look at a little bit of the history of the PMP^® exam, the PMBOK^® Guide, and the scoring of the exam.

The PMBOK^® Guide 2000 was first released on 12/1/2000, The PMP^® Exam was not based upon this release until 3/4/2002
At that time the PMI^® published passing score was 68.5% (137/200)

The PMBOK^® Guide 3rd Edition was first released on 10/31/2004, The PMP^® Exam was not based upon this release until 9/30/2005
At that time PMI^® had published that the passing score was changed to 80.6% (141/175)