The currency support that hit the AU beta a month or two ago was the big one for me, but the low rate (1.75% + 30c for Australian cards) is a nice touch for those who might normally smash their heads against a bank's merchant API, PayPal or someone like eWay (who I don't have nice thoughts about).
What would be an example of a traditional rate with other merchants in Australia?
PayPal Express Checkout starts at 2.4% + 30c (across all trans). One might use PayPal for other reasons than just their fees (i.e. your user demographic) but their API is still a mess.