I purchased a copy of the 2011 NEC in PDF format and I was able to get it to open on my Mac. You have to use Adobe Reader and you have to install the FileOpen plugin to Reader first. If you try to use any other PDF viewer or Reader without the plugin it won't work. The NFPA has put a lot of copy protection on this pdf and it makes it difficult to use.
One thing to keep in mind if you are thinking of buying this is that you cannot add comments or bookmarks using Reader, so all you get it a large PDF file with very few built in bookmarks and you spend a lot of time scrolling through pages to get to where you want. You can add comments if you use Acrobat Pro but that is about $400. I would not have bought it if I had known this.
