I was watching the credits on Brave and recognized a couple of Animation:Master alumni on the Pixar crew (Pixar has a proprietary software, not A:M)–Barry Zundel was one of them. Barry has been writing a series about software usability on his blog, and had this to say about A:M which he used while working at Avalanche Software :

…In the ensuing years, I used A:M exclusively and came to understand what “usability” really is. It is still one of the best examples of a truly non-linear pipeline ever. Nothing that I have tried has ever come close.

I have to wholeheartedly agree with Barry on Animation:Master’s usability! Barry also has a series of A:M tutorials available on his website that I highly recommend.