In Australia's history, of 44 constitutional referendums held, only 8 have passed (3 of them in the same ballot). It's very difficult (some would say, too difficult) to amend the Australian constitution, and definitely not something that tends to happen with a "swell of public sentiment".
Compare that to 11 amendments to the US Constitution over the same period (1901 onwards) - two of which I'd point out dealt with the introduction and repeal of Prohibition (which I'd say qualified as a "swell of public sentiment").
My state, like a few others in the US, has voter initiatives that become constitutional amendments. The last one that made the news was the one that made it illegal for me to get married.
Another initiative from a few decades ago is a major part of why California can't raise enough money to fund itself now.
So yeah, I'm not a huge fan of ballot initiatives.
