What kinds of books are you interested to see for Longhorn?  What types of developer books would you like to see?  Also, what types of "power user" books would you like to see?  What do you think of Brent Rector's book if you've seen it?  There is a lot of talk about all of the Longhorn book projects that are in the works, and I've had some great discussions regarding a collaborative effort for a Longhorn book as well.  I'm curious to see what people are thinking in this regard.