Received the 20% off code via email but looks pretty generic. You can become a 'Citizen' by signing up for an account.
Terms and conditions: 30% off is a combination of 10% Bookworld Citizenship discount plus 20% promotional offer; offer is only redeemable on books and excludes CDs, DVDs, Blu-rays, eBooks, eReaders, stationery, calendars, gifts, accessories and Bookworld Gift currency. Promotion is only valid on Australian RRP titles; offer valid until midnight (AEDST) Wednesday 25 June 2014.
Can confirm it works. Just now to decide whether to pull the trigger.