OMG A KEEPER!
those other tutorials should stay blammed forever! This one pwnz!
Now enough of that, the only thing that you didn't take much thought into was explaining the masking part. I don't have the actual flash program, so I guess I'm missing something, although you should have done a better job of explaining it. Also, the cinematic slides in your last tutorial needs working on. Last but not least, your flash is a little on the heavy side in the lag factor compared to the overall average lag of the other flash movies, of which I should say runs pretty smoothly on my crappy computer.
BTW, I found all three major easter eggs! Mwahahaha! One's a sound test (tell nobody!) another gives the history of the games which you borrowed music from (which also contains a message pointing to the sound test) and the last one has the statistics of each of your animations. By "easy to find", I think you actually meant using the cheapo button though. Ever thought about proofing against that? (it's possible, but then one of the easter eggs would be disastrously hard to find)