Well, I got brave and tried out Google Australia Books. It turns out to work well.
On my Windows PC I used the link provided by iandix (
http://books.google.com.au) to buy the book.
With the wi-fi running on my iPad, I launched the Google Books app. The book cover was sitting there with a "Download" button underneath. I clicked on the Download button and the book downloaded to my iPad.
The Google Books app has some sour reviews on iTunes. I've only downloaded two free books and a paid-for book so far. I haven't experienced any problems. The Google reader is basic but good enough.
So...any Aussies wanting to use Google Australia Books - avoid the Dymocks website with its higher prices and go directly to the google website.