That's a loaded question with respect to Sydney. Your best bet is to read this:
http://www.airservicesaustralia.com/...ney/200803.pdf
It gives you a basic look at the Long Term Operating Plan (LTOP), aka. noise sharing.
It also gives you an idea of what runways are used when.
To cut a long story short though: parallels in the morning peak (about 7-11am) and evening peak, and some form of crossing mode at other times, and then curfew at curfew time.
Makes an interesting read though.