How accurate, or reliable is Fathom's Keyword Price Index?

It seems that it's given a lot of credibility in the advertising world. However, IMHO I think otherwise. I wrote a post shooting it's relevance full of bullet holes. One of my reasons is that their data must come from their own client base. Without re-writing the whole post, you can read it here: shimonsandler.com/?p=288

Can anyone prove otherwise?