The way I see it certain areas will be more affected than others.
To say that all prices will fall by 50% is incorrect. Sure in certain areas they have fallen by 50% but take a look at inner city suburbs, they have only grown. Alot of areas that are within 5 - 10Km of a major CBD like sydney have had at least 10% growth last year alone.
Now when you move further out of this area it starts to become a different story, the Kellyville example doesn't surprise me. If anyone is familiar with Sydney, Kellyville is quite some distance from the CBD and with no rail transportation it really amazed me why people were almost paying $1mill for a house.
It all depends on 3 things, location, location, location... When you have that in property then you will always be okay provided you haven't overextended yourself in debt.
Some houses will fall and some will rise. A general statement like house prices will fall by 50% is wrong and very misleading.
It depends on the area... A correction in price for some areas is really needed as there is alot of speculation built into the price, however you will find that anything that is within approx 8km of a CBD like Sydney will not fall by 50%.. Too much demand.