Don't think you get passport stamps anymore -- I was just in Oz last December and wanted to use the SmartGate lines (US passport) but the kiosks were down so I had to use the conventional immigration lines. I was surprised not to get a stamp and asked if they would stamp my passport since I might apply for AU citizenship in a few years & would like the proof of time in country. They told me that everything was electronic & they didn't even have the stampers any more.