I hope I'm one of the targeted audience members for the book. I've used hadoop, done clustering (not with Mahout), have read about collaborative filtering, and plan on using Mahout in a business intelligence setting in 1-2 years. However, I've never used Mahout itself. What I would like to see is more of a cookbook style. I want to know the whys, not just the hows. Why should I normalize data in a certain way before clustering it, what happens if I don't, etc.... I've read Collective Intelligence in Action and found it pretty much useless - I don't need another survey on the topic. Instead, I want to know the ins and outs of mahout so that when I go to sell it to someone I can answer any and all of their questions around it. If you want an introductory chapter on the topics, that is fine, but keep them short and point to other materials.
Thanks! Tanton