I just noticed this while looking at my points transactions in the Cinebuzz page. So I am aware that there is this bargain going on now which is earn double points for movies that you watch until the end of August:
http://www.ozbargain.com.au/node/29181
Anyway, just pick a movie that you want to see and pick the session you intend to watch, and free tickets should now cost 50 points and not 100 points. I have no idea when it expires, but maybe an educated guess could be when the double points offer ends (end of this month, link posted above). Make sure you are logged into Cinebuzz.
To put this into perspective, combining this with the double points offer currently on, that basically means every 2.5 movies you watch earns you a free movie!
And something that I did not know until recently, and since we're on the topic I think I should mention this. Cinebuzz points expire 2 years after you acquire them. I only got Cinebuzz because I thought points didn't expire. I don't watch movies regularly. Luckily it's been less than 2 years (but almost) since I joined, so I'll have to use up my almost 200 points soon!!
edit: Another note, unrelated to this deal. Maximum of 40 points per day per member. This, and the 2 year expiry point information, both from the Cinebuzz FAQ.
Great post! Thanks for the heads up about expiry.