I REALLY like Robert Boyer's eBooks. You will learn more about A3 reading those than any other source. He does not go into the "what"... but instead focuses on the "why". He helped me out a lot on Apples Apperture discussion forums... but his eBooks really made the difference for me. I just read them again on a flight to Hawaii yesterday... and learned a bunch of new things. I also enjoy just reading his blog.
I recommend you get the A3 Organization, and A3 File Management ebooks. They are an absolute bargain... and it will open up A3 for you.
Today I found this site and it's quite useful what Thomas shows his audience. Found some great advice about tools of aperture.
Hope this helps a bit!!!
KA