Don and Sam beat me to it.  The first Indigo book has hit the shelves: Programming Indigo : Code Name for the Unified Framework for Building Service-Oriented Applications on the Microsoft Windows Platform Beta Edition by David Pallmann.  I'm ordering my copy today ;)  Also keep an eye out for: Inside "Indigo"--Infrastructure for Web Services and Connected Applications by Jason Clark.  It looks as though it should be coming out soon as well.

Happy reading!