What prompted me to question this was my coworker said it was a best practice when showing me a database design. I remembered Paul's video from an earlier viewing but I didn't remember the details. So, I viewed it again and did the demo myself so I saw his point.

Is there a white paper or some reference material that states this as fact? Not that I don't believe you, and given what I saw in Paul's video and other blogs, no, I would not use a GUID as a PK. I just need to help someone understand this at work.