According to the advertising system, Facebook has around 1.5 million members in Australia, or over 7% of the population…
(The US has 20m/6%, Canada 7.4m/22%, the UK 6.4m/10% and NZ 200,000/5%).
If you want to see some numbers for yourself, just look at the [Facebook Flyers](http://www.facebook.com/flyers/create.php).