The uphill is quite a few programming languages resemble the grandfather languages that have been around for decades, like C. Once you know one language you realize many other languages resemble each other to a great extent. Once you learn one language it's much easier to learn another and unfortunately that's where I feel books fall flat. Often authors will say something like "If you know [some language] this will look familiar"..
I have Moock's book and while it's ok I didn't really think it was out of the ballpark on complexity. I honestly don't think it's a bad place to start but he will bring you up to terms on programming concepts that apply to many languages, like the term you'll see over and over, Object-Oriented Programming (or OOP).
My vote is a combination of video training, online tutorials and forums.
Here's a very well known forum and site that has AS3 tutorials (scroll down to "ActionScript Basics"):
http://www.kirupa.com/developer/flash/index.htm
Aside that I think video training by the ultra cheap ($20/mo?) Lynda.com is invaluable. You'll not only learn AS3 but a gazillion things about every subject and software you can imagine. I've learned heap tons there. The price is absolutely worth every penny and I think video is one of the best ways to learn:
http://www.lynda.com/search?q=actionscript&x=0&y=0
There's plenty of designer courses on Lynda as well and I bet you'll learn as much or more about Flash Design concepts as you do AS3, all for one low price. In Borders it'd probably cost between $39 and $59 for a decent book and that's 3+ months of video training.
As always, post any questions here about AS3 concepts and we'll be happy to answer.
