Aussie Post's tracking numbers are pretty useless. Most of them are internal tracking numbers that consumers don't have any hope of using.
For some items (Express Post), the tracking number can be used, but they only scan items when they leave once centre, then scan again when it arrives - but most of the time the database is only updated once the item has been delivered.
The hassle of using Australia Post isn't worth the $5 saving compared to using TNT or Australian Air Express.