Considerably more. Take the new Powerbooks that everyone has been talking about as an example. The 12" model in the US store retails for US$1,799 while the same model in the Australian store goes for AUD$3,995 (which at todays exchange rate is US$2,306!). Sure you'll need to factor in some shipping and what have you, but a difference of US$507 is not something to glance over, well at least not for me.
For the record the price comparison between the entry level iBook yields a US$265 difference between the two nations.