Boy, I'm a total monster book glutton, but I'm really not sure about this one. The preview monsters didn't do much for me, nor did the monster lists, and I'm not running Eberron, either. And I'm really concerned about the reports of editing problems. (I know that WotC has already made changes in their QA/QC procedure based on past gaffes, but what books benefit?)
I wonder if we have finally hit total d20 monster saturation, the point at which every new monster is just (a) a pale variation on past monsters, (b) a powered-up, kick-ass version, or (c) a heavily world-specific variant. It's like a beholder, but this one is /purple/! This is a /blood/ troll, and it has 20 HD and a vorpal bite! This is a halfling, but they're called mu-shus, and here's six pages of loving description of their culture and history in the World of Gorth!
I understand that fourth Monster Manual is under development. And a Tome of Horrors III is in the works, and even though I am a huge fan of the first two ToHs, I'm really not excited about the idea.
Now the Monster Geographica series, on the other hand, is a different story -- culling through exisiting monster books, pulling out worthy candidates and updating them to 3.5? /That/ seems like a worthy project.