I did see some official statistics a few years ago on distance travelled.
Figures varied by state and were all within 13,000 - 16,500 km per year from memory. Tas was the lowest for fairly obvious reasons but I can't remember which state was highest.
A lot of people say 20,000 km is normal, and a lot of vehicles do travel that far. That's the distance a lot of fleet leasing etc is based on. However, the official average takes into account the significant number of very low usage vehicles which brings the average figures down.
Total petrol (not including diesel, LPG, kero, fuel oil etc) consumption is somewhere in the order of 1000 litres per head of population per annum. That includes children etc who (hopefully) don't drive cars.
As for me, petrol prices don't bother me overly much since I only buy about 350 litres of the stuff each year at most and I could cut that down quite a lot if I had too. It's a major expense for a lot of people, but not for me personally.