To be clear, I haven't had to deal with E3 related issues for 7 or 8 years and the subtle details of it have probably changed. Hopefully you never find yourself in a position where your E3 becomes invalid unexpectedly but if so, speak to a lawyer to find out the current gotchas and how US Immigration interprets the laws. (Or look at http://www.expatforum.com/expats/america-expat-forum-expats-... - it tends to be an excellent source of typically up to date information.)
Pro-tip for Australian's living in North America (or anyone crossing the Pacific, really): Qantas/OneWorld (and maybe other airlines) typically doesn't charge one penny extra if your North America <-> Australia route includes a stop in Hawaii. Hit up hotwire.com and find a cheap hotel in Waikiki and it's the absolute perfect way to break up a 14+ hour flight.
My parents are in Perth, so Emirates via Dubai is a slightly better option. Emirates are typically cheaper and their stock is nicer. Plus each of the legs is shorter than the trans-Pacific marathon.
Mind you, living and flying in the US brought an unexpected phrase to my lips: "I miss Qantas".
Pro-tip for Australian's living in North America (or anyone crossing the Pacific, really): Qantas/OneWorld (and maybe other airlines) typically doesn't charge one penny extra if your North America <-> Australia route includes a stop in Hawaii. Hit up hotwire.com and find a cheap hotel in Waikiki and it's the absolute perfect way to break up a 14+ hour flight.