Yes, it was just proving my citizenship and a slap on the wrist. The stamps are probably the biggest loss - but can always visit those countries again. Note to self: bring driver's license and Medicare card on future trips overseas.
Another dual CAN-AUS citizen friend of mine has a sketchy track record with her Australian passports (has a reduced validity limit now due to multiple losses, and once came home with an emergency passport and jetted off again with it without applying for a proper passport...). She relayed to me advice she's received at one consulate that some airlines can deny boarding as technically they have a duty to ensure correct immigration documents are in place. However, if you get there early and explain what happened, and they call the relevant authorities (for example, in Canada the border authority deals with foreign passports that are found) and you show some proof of Australian citizenship, they will sometimes let you through. Qantas are fairly lenient, while Air Canada reportedly has denied [return to Australia] in the past. Problems arise if you transit through the US.
There was an article recently published on attitudes towards flag carriers. This is one of the reasons your own flag carrier comes in handy I guess. I didn't have any issues at the gate, but had there been issues with check-in or boarding at least I was flying QF.
My friend also says you can't just get an Australian ETA on a foreign passport and return like that (though I don't know if this is a 'well you shouldn't' or a technically can't).