I purchased the 2011 and 2014 NEC libraries last year. One of the best investments I have made in my career. I listen to it in my truck and call it truck college!
I really like Mike's way of explaining the Electric Code in the Detailed Code Library - it helps us to understand through the use of pictures.
I purchased the Detailed Code Library. What I like the most, is that Mike and the panel break the Code down to a shop floor language.