The YT video says it's private.
It's interesting that there are these different "difficulty settings". I'm thinking that the fourth group, people who already have experience with flixel, is probably not really required at all.
I was really annoyed by how many download links I was forced to click. First of all, I don't want to be forced to click on a FD-installation if I already have it installed, so, there should be a "skip" button there.
At the end of chaper II, there's a download button even though it seems to be a simple proceed button.
I personally didn't find the text-writing-effect or however you wanna call it very suitable. It's a tutorial, not an RPG. Same for the screen flashing, you should be able to turn that stuff off entirely.
Another thing that might be worth considering is using another, more readable font. Not a huge fan of the pre-installed one in flixel. Also, I think you're using a scale level of two on a relatively small resolution. Since this is a tutorial, I would try to fit as much information on the screen as possible.
It seems like the right page of the book graphic isn't used at all. I'm thinking that could be used for code, which is explained on the left. Also consider doing syntax highlighting. You could also use that page for screenshots of FlashDevelop or to demonstrate things.
In my opinion, it's a must-have feature to be able to access chapters individually.
You should probably disable the flixel debguger.
All that being said, I really think that something like this is a great idea, especially for people who are completely new to making games / programming and flixel in general, because they are not the ones who are going to seek out tutorials. Actually, this is how I myself got into it (Shootorials on Kongregate).
Btw, good job on Utopian Mining. Enjoyed that game.