There is not yet a maps.google.com.au, and searches for Australian locations yield little ("melbourne australia" will get you on the right page, though anything below that, like, say, "northcote australia", a street name or a post code, draws a blank), though if you go to the US, UK or Japanese site and drag, you can get to the wide brown land with green bits around the edges.
It is quite complete (Check out the detail of the Birdsville track around the SA / QLD border - you can't get much more remote than that), but it's really no different from what has been offered on Multimap or Whereis for years now. Well, the property boundaries are nice. And the Google interface is nice. But I don't for the life of me understand why it took them so long to get their hands on the dataset.
Multimap and its ilk suck dead bunnies through a straw. The window's too small, clicking on arrows to move around is bordering on play-by-mail map navigation, and the area around the window tends to be spammy with ads and promotional links.
It includes obscure QLD mining towns (I looked up my old place) so I'd say it's pretty complete.