Once you take postage out of the equation (which they do) then I still prefer a paperback to an ebook (though ebooks also have their advantages)
Sampled a few book prices vs Dymocks (as they are one of the leading Aussie booksellers) and Seekbooks.com.au. In the case of Dymocks you need to add cost of time and fuel needed to get to a store. For Seekbooks.com.au you still need to add postage costs.
Recent bestsellers, if discounted at Dymocks are about line ball but still worth testing the difference on.
Here's some that show the stark difference
Ian Rankin's Doors Open - published 6 Aug 2009 paperback
GBP7.19 A$12.72 from Book Depository in UK
A$22.99 from Dymocks
A$20.69 from Seekbooks.com.au
Val McDermid - Beneath the Bleeding
GBP6.29 A$11.13 from Book Depository in UK
A$19.99 from Dymocks
A$17.99 from Seekbooks.com.au
Tim Winton's Breath - paperback
GBP7.19 A$12.72 from Book Depository in UK
A$24.95 from Dymocks
A$22.46 from Seekbooks.com.au
The last one is crazy - you can buy an Australian author's book in the UK and ship it to Australia cheaper than you can buy it from a local bookshop. Even the hardback version from UK is cheaper than the Australian sourced hardback.
I haven't used Book Despository to date but I will be placing my first order ASAP.
Works really well at moment given strength of A$ vs GBP but there is enough margin in there that it will still make sense when/if A$ weakens.
Update: Should have found booko.com.au first - it makes the comparison
shopping for books across multiple sites really easy and automatically
converts back to A$. I can myself buying more books - but what about
the great pile of unread ones to tackle first. Need more hours in the
day.