According to Mike Downey and Ryan Stewart, Colin Moock's Essential ActionScript 3.0 is the bestselling O'Reilly book and number four (or five now?) on Amazon's best seller list.

I had previously posted about my problems finding a copy of the book, including the major delays by Amazon.com. Apparently others are having the same issues (see the comments at the bottom of Mike's post), which I am sure is a result of unexpected popularity on Amazon's part. Either way, if you are still wondering why you can't find a copy of the book -- now you know!