I am currently reading the first chapters of a Powershell book called "Windows Powershell in Action" written by Bruce Payette.
There are currently Five chapters available and I am done with the first two. It's very well written with lot's of examples and a good explanation of how Powershell works and what the different parts means. I like the fact that in Powershell you can create aliases of commands which can make a script more- or not readable at all. So be careful when using aliases or describe your aliases in comment within your script, you will remember them tomorrow but maybe not next month.
You can download the first chapter here. If you want to know more about this book go on to the publishers site: Manning Publication
I will definitively continue reading the next chapters as I receive them.
Speaking of Powershell Bart De Smet a Belgian MVP wrote a very cool post about how Using System.Windows.Forms.MessageBox in PowerShell.
Another very good Powershell blog is "/\/\o\/\/ PowerShelled" where he actually links to a video of the author of the book I am reading. He also wrote (11 now) different blogpost about Powershell and Active Directory, check it out very very cool.
I know most of you already know that we Released To Web (RTW) Windows Powershell 1.0 for Windows XP SP2