Well as a born and bred Aussie I grew up with Yds, ft and inches, then someone with wisdom/intellect or whatever, decided we would go metric.
When I was working I had the issue of measuring a job in both.....don't ask me why but I tended to use the metric for larger measurements and imperial for the smaller measurements.
Either way, it depends on what we were bought up with.....Imperial rules!!!!
Best bit is in the Hardware stores and the young ones talk metric ....I ask them to speak english.
Khris