I did an online PDC and I'm really not sure! I did it mainly so I have some sort of certification for designing landscapes and to force me learn things that I might not be so interested in on my own. I'm implementing the first design for my portfolio right now.
As it was online I got no hands-on experience from it and I also didn't receive any feedback on my design. Some of the backyard designs that passed seemed really really simple and something that anyone who's read a few thousand words on Permaculture could do. This was my main disappointment - could I have done more work or done anything better? Did I do anything that was feasible yet impractical? Was my implementation plan realistic? I didn't even mention the ethics in my design.
I also echo the comment about how most of the course wasn't relevant to my local climate (UK). There was a 20-30 minute video on temperate climates and a few references back to them in other videos. Most of the focus was on warmer/sub-tropical climates. I don't regret doing it for the certification but I think in retrospect I should have spent my $1000 on a 5 day on-site UK course that enabled me to get my hands dirty and use a few earth moving machines.
From all this, I think there is a big opportunity for experienced PDC teachers out there - offer an exam or a service that enables people to get certified just by submitting a design rather than watching videos as well. This way people could be judged on their designing ability without having to buy a $1000 course of videos. On my course they had no way of knowing if I actually watched the videos, so someone should just offer the certification service.
So, bearing in mind that you can source and talk about Permaculture information elsewhere, you are basically paying for the certificate and the certificate's main uses are (A) to start teaching others Permaculture or (B) get work as a Permaculture designer. If you don't intend to do either, I question the point in doing a PDC.