If you like your Google Play Books but have been wanting to pre-order them then Google Play has some good news for you overnight they sent out a tweet stating that you can now do just that :
— Google Play (@GooglePlay) November 28, 2012
They elaborated further on how this will work on Google+ :
Can’t wait to get your hands on Tom Clancy’s Threat Vector (US- goo.gl/hh5pR) or Douglas Preston and Lincoln Child’s new title Two Graves (US- goo.gl/UP8dt)? Starting today, you can pre-order books on Google Play (goo.gl/TgoEO) where Play Books is available. Place your pre-order and once the book becomes available, we’ll charge your card and send you an email notification letting you know that your new book is ready to read.
Now the links they supply to books, unfortunately show no button to pre-order so whether this option to pre-order books is just something that is not live yet in Australia or just that I haven’t found any books to pre-order yet, I`m not too sure but I have a few books that I was looking to purchase down the track and I searched all of these and couldn’t find any. Let us know in the comments if you’ve found some books to pre-order.