Have you looked at the aircraft order announcements from Tiger, Virgin, Jetstar & Qantas? Between them they plan to add hundreds of extra aircraft to Australian skies over the next few years... Sydney, Melbourne and Brisbane will seriously struggle (as they all do now at certain times of day and under certain wind conditions).
Parallel runway is planned for BNE but won't be finished until about 2013. Melbourne needs parallel runways and they should have started building those yesterday. Sydney will need something - but nobody seems to quite know what.