I thought it was 30... yep, just checked the agreement. It says the following (paraphrased):
You can work 30 ordinary hours per week if you're a casual. However, for a period not in excess of 4 consecutive weeks, you can work for 38 hours.
That's from the WA SDA agreement.
By the way, if anyone's lost theirs, it's actually available online from this site:
Collective agreements - made after 27 March 2006
Search for 'woolworths' and scroll down to the bottom half of the page. The NSW/ACT, Qld and WA agreements are all there (not sure about Victoria, didn't check. May still be under Safeway but I'm not sure).
Speaking of agreements, when's that national one supposed to appear?