Welcome to the Q&A Forum

Hi Drew, In general, we'd say to use one English language domain to target all English speaking regions, but since you have a .com.au domain, you won't be able to use this to effectively rank in the US. It is possible to mirror a domain and geo-target each so that they rank well in their intended locations. You would set the geo-target for the US site to the US in Webmaster Tools (the Australian site is automatically geotargeted because of its ccTLD). Google reps have stated in the past that this is effective and will eliminate the duplicate content problem. Of course, Google isn't perfect and sometimes this goes wrong. We had a client with two identical websites--one for the UK and one for the US--whose UK site always showed up in the US and whose US site ranked nowhere in either territory. That's very uncommon, however. If you do this--mirror the site and properly geotarget in Webmaster Tools under Site Configuration -> Settings--neither version of the site should find itself removed from Google due to duplicate content. Keep a very close eye on each site's indexation, ranking and traffic though. Like I say, this method isn't perfect as Google has gotten it wrong in the past. Cheers, Jane