I'm a huge fan of Moz, they seem to simplify SEO, the problem I have is figuring out the difference between page authority, and domain authority. To me, they're basically the same thing? Or am I missing something here?
PA is Moz guess at page rank for a page, the DA is the authority the domain has.
I say guess as they can only attempt to come up with a score similar to page rank but please remember this is not a google score.