Geocaching Australia uses your home coordinates to calculate the distance to caches and also plot on maps which are available to the public.
Please use WGS84 in degrees and minutes. See coordinates for more information on this.
You can omit the degree and minutes symbols if you wish, eg: S33 12.345 E151 12.345 should work fine.
If you are are worried about geo-stalkers, put in the coordinates for your local pub or just make the last few digits zeroes to round it off.
You can change your home state by visiting http://geocaching.com.au/my/settings