I read a couple of years back in a car mag about a guy who was banned for undertaking, think it might have been an old Max Power issue with a GSi Nova (was in the reception at my old job, honest! )

We are allowed to do it here and it still scares the crap out of me doing it. A lot of cars zip between things but it isnt pleasant being sandwiched between two trucks not knowing if either have seen you. You can also remain in the right hand lane around cities here but not officially supposed to on highways.