Please note that everything said here is my personal opinion and NOT an official endorsement by Pixologic. 
The advantage to Flash is that over 99% of computers at this point have Flash Player already installed on them. It is truly cross-platform, and has the advantage that it displays precisely the same regardless of operating system or browser. That’s actually why I developed my website in Flash; not only did I have better control over what things would look like, where they would be, and what they would do, but I also knew that it would look exactly the same for everyone. As someone who has programmed HTML for years and seen Netscape or other browsers slaughter some of my work unless I built alternate versions with autodetect javascript (which itself doesn’t work in all browsers), I can’t stress enough what a huge benefit I found Flash to be.
The place where I actually learned the most in the shortest period of time was a book called “Foundation Flash 5” published by Friends of Ed. They now have “Foundation Flash MX” as well. It’s well worth the investment!