More important on the Sydney Canberra run which most of you seem to overlook is why do Qantas run so many Dash 8's to Canberra.
The reason is that a 737 needs to be 120% full to break even on the route. Even with Virgin's lower costs you would not make money even if you were full every sector, and with the fares being advertised they are obviously just doing something with the aircraft between other flights.
Qantas only put the jets on a few times a day to fulfil the need to have some business class seats on the route. Ansett were the same, so Virgin will probably never expand much to Canberra from Sydney unless they have some spare money to lose.
PS. I think 30 minutes, 22 seconds is the quickest I have seen CB-SY in a DHC8-200, with a landing on 34L!