I've heard good things about Lynda.com training. I've considered it... but haven't yet.
I really love the Boyer books. They are pretty small, but jam packed with just the right data. I often go back and re-read them even after using Aperture for years. Boyer has [well justified] strong opinions, and focused on the "why" to do certain things... rather than being a boring instruction manual regurgitating the functions of buttons. For me (and maybe for my personality)... I think it set me off knowing the Aperture fundamentals.
Because I've never signed up for Lynda.com, I am not in a position to compare them to ApertureExpert. Joseph does a good job on the videos... and I've learned a ton from each one that I've watched. At only $2 a pop... it is a bargain.
/Jim