Whoops, looks like the secret is out-- now you know why I've been crazy heads down this month. Look what you can (pre-)buy on Amazon!
It's on Amazon: http://www.amazon.com/Learning-MCollective-Parallel-Server-Management/dp/1491945672
At the O'Reilly website you can buy Paper or E-pub copies, or both for a combined price:
I highly recommend getting an electronic copy. It's hard to push updates and revisions out to a paper copy....