We do it in my sister's estate similar to how Leetieeb described it. We put notes and balloons in the neighbours letterboxes the week before and tell them to put the balloon on their postbox if they want to participate. We have been doing this for 5 years running and it has become HUGE- at least 50 kids come from all around to participate and SO MANY of the houses put out balloons that last year was the first year we had to stop trick or treating (too many bags of candy) before we got to them all!!
My sister and I grew up in the U.S. I don't understand the Australian aversion to the holiday. It's the MOST fun holiday of all. I am glad we have carried on the tradition with our kids.
I am going as Carmen Sandiago this year!