Introduction to the Exchange Management Shell has been recently refreshed.
Overview: Microsoft Exchange Server 2007 introduces a new management platform called the Exchange Management Shell, based on Microsoft Windows PowerShell, formerly codenamed "Monad". This document outlines the key benefits that the Exchange Management Shell provides to Exchange administrators and developers, and explains how cmdlets are structured, and how data is managed.
If you're interested about the new Exchange management capabilities through PowerShell (and I'm sure you do), there's another nice document for you to read: Exchange Management Shell Quick Reference.
And for those who want more, you may consider Windows PowerShell Quick Reference, from O'Reilly (Its author, Lee Holmes and O'Reilly were so kind in providing me a copy, I'll promise I'll post here a review as soon as I have some time)