Under the boating regulations we are required to wear PFD when more than 400m from the waters edge.
http://parkweb.vic.gov.au/__data/assets/pdf_file/0010/527527/Guide-to-Kite-Boarding-Port-Phillip-Western-Port.pdfwww.transportsafety.vic.gov.au/__data/assets/pdf_file/0009/41121/Victorian-Recreational-Boating-Safety-Handbook.pdf (page 61 or search for kiteboard)
I'm not being the fun police. I don't care if you wear life jackets or not. But, if I was in the Water Police I could probably ignore the odd kite boarder without a life jacket. If I saw 25 people in a bunch with no life jackets I would feel obliged to book them if only because Marine Safety would kick my arse for not doing it.