It was not so big in Australia when I was a kid, but with the increase in US culture throughout our media it has become quite a celebration... lots of lollies for the kids and fancy dress parties for the grown-ups.
But it had no special meaning to most of us down under, just an excuse to let our hair down for a night!
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Computer Lie #1: You'll never use all that disk space.
"I love deadlines. I like the whooshing sound as they fly by." - Douglas Adams