Just a quick FYI - according to Gamespot, Portal will be available as a free download via the Steam Storefront until September 20.
I can't say for sure whether the offer is valid for Australians (as I've previously purchased the game), however, Kotaku AU has verfied the story.
If you haven't played the game before, I would urge you to take the plunge. It's not like it will cost you anything!
Have a good weekend. What are y'all playing?