I haven't been able to bring myself to pick up the PFB. Flipping through it at the store, it simply didn't pull me in, and the price definately turns me off.
Monsternomicon on the other hand, is a beautiful, extremely useful book. Despite the fact that folks who obviously aren't very familiar with it will tell you that it's a "steampunk" monster book, less than half a dozen can really, in all fairness, have that label. The monsters all have play hooks just jutting from them at all angles; it's so easy to use a Monsternomicon creature in your campaign that it's not funny.
I will, however, concede that it has a few too many monstrous humanoids. Because I'm about to start a new campaign, I've been flipping through all my monster books, making lists of what I'd potentially use in this campaign. The Monsternomicon probably has the longest list, but the monstrous humanoids are not on it.
But dude, the Monsternomicon dragons! Those alone make the book worthwhile, IMO. I haven't been that excited about dragons... well, ever, Draconomicon included.