I just "won" a $100 voucher on Webjet as well. Unfortunately these are only available for purchasing certain "exclusive" Webjet content that are at least $500 so I'm not bothering putting it down as a win.
I also won a $50 Webjet voucher today and noticed that the voucher expires on the 30th April 2015. Not much time to plan a trip and use it. I don't think I'll bother either Ross.