DIAC will know you're here as soon as you go through passport control in Australia. It's the state/regional sponsorship visa's that require you to notify them of your whereabouts...
Saying that we were on the old STNI (PR, State sponsored) and never had to let SA know - at the time I think it was only the SIR (Temp, State sponsored) that had to...
Obviously no harm - no foul, as nothing was mentioned when we went for citizenship ;)
We are on a 475. Our meet and greet gave us a form to fill in to send away to the department, however, on our visa we were invited to attend a free seminar at 55 Currie Street, on finding work in SA. We went to this and we just filled the form in there and then and the lady took it away - not heard anything since. If you have change of address or employment you need to always let them know.
I would definately recommend going to this seminar if you can - it explains what you need for PR!