I wouldn't recommend this unless you're disciplined with your finances, but it really does work
Interest on $10,000 for 12 months at promotional rate of 0.99% - $99
Interest on $10,000 for 12 months at mortgage rate of 6.65% - $665
Saving $566 per year by doing a balance transfer onto another credit card, using that balance for everyday spending and putting cash in an offset account - priceless
What really makes it work is you don't need a credit card debt to do a balance transfer - they will happily transfer into a debt free card giving you a credit balance.
One day I will have a black mark against my name saying not to offer me any more balance transfers.. but until then I will let them pay for my car rego each year.