I've been getting a few questions like this in my inbox:
First of all - thanks for the love! Now, here's the lowdown:
Learn Windows PowerShell v3 in a Month of Lunches, 2nd Edition, probably overlaps with the original book by about 70%. Every chapter, however, has been updated with new information for v3. The assumption is that you're learning PowerShell from scratch with either book, so there's no specific callout of "new stuff" for you. There are also entirely new chapters intended to provide better education - including one chapter where my new co-author and I focus on techniques for stealing repurposing other people's scripts, since we know that's a common task. There's also a whole new chapter on regular expressions, a new chapter on combining what you've learned to complete a practical task, and so on. But this isn't a "just the differences between v2 and v3" book; I tried writing a "Delta Guide" like that once, and met with mixed success.
You will, however, notice that the new Lunches book actually omits some information. Gone are the chapters on error-handling, debugging, and building advanced functions; the new book shows you how to build a parameterized script (not a function) and stops. That's because there's an all-new, full-sized Learn PowerShell Toolmaking in a Month of Lunches coming (watch http://PowerShellBooks.com for links). That takes you through those scripting topics - error handling, debugging, modules, advanced functions, and much more - in a much more thorough way, using a much better build-as-you-go narrative. Think of it as the "sequel" to the original Lunches book.
Hope that helps you figure out which of these two books (or both!) best fit your needs. And don't forget there'll be a pre-order for both of them, starting August 1st, which will only be available until the books are finally published.