Looks like the new PowerShell Development book from Wrox is out. You can view the details HERE.
What's cool for everyone is that Wrox has made the source code available as a free download. There are some comments in the source code also. So, for people looking for more development examples, beyond the PowerShell SDK, you now have them.
This book assumes the reader has a relatively good base of C# experience. I've written a cmdlet or two, and this book will definitely challenge me to go to the next level and beyond!