I started the Diploma through the Permaculture Association in 2008 and finally accredited at the London Permaculture Festival in July 2013. The diploma process is Action Learning personified. After you have completed a Permaculture Design Certificate you can apply for the diploma and are assigned a tutor who is more a mentor than a teacher. This is a fantastic way to further your permaculture development.
You can download some examples of my projects as word documents for free, I offer this to help encourage others to take the diploma and then share their knowledge and experience onwards too.