This will put you straight... (read the whole thing or just the article at the end)
http://sheldonbrown.com/brakturn.html#bikeculture
I agree Sheldon's article pretty much covers all the physics involved. But after recently reading it for the first time I wanted to immediately respond (unfortunately can't now Sheldon is no longer with us) cos I believe Sheldon overlooked the main point made by RDV4ROUBAIX's above (although also an important fact in non-race scenarios). The point is that with modern STI levers it is very useful on open roads to be able to brake suddenly with full grab front brake using the left hand (thus achieving better stopping power) and to be able to change down gears quickly with the right hand such that it is possible to accelerate again in a reasonable gear. An example is when approaching lights changing to red or when avoiding a car that's braking in front of you. As Sheldon pointed out in a situation where you need to brake quickly then having both hands on the bars to brace yourself (a necessity for rapid deceleration via front wheel braking) is far more important than throwing an arm out to indicate a right turn.
I have never heard of right vs left front brakes being enforced as a requirement in Australia though. That is is news! Never knew I was ridin' outlaw. However the Bicycle Victoria link provided by Argon Man appears to not be working anymore.