Some recipes like quiche or Caesar salad (without chicken) absolutely need bacon in my opinion. Where bacon is just used for garnish it can be easily left out.
I've tried the vegetarian bacon available from supermarkets and it you use your imagination it could taste a little bit like bacon .. but the ingredients list is quite long and I wonder how healthy it is for you being so processed. (And yes I know that bacon is not necessarily healthy either!)
I've read that strong tasting mushrooms might be an alternative so I'm keen to try that in a quiche but I'm concerned about what happens when the mushrooms cook and shrink in the quiche.
I've tried turkey bacon in the past but I've never seen it for sale in the shops. If it was widely available I think that would be a good answer.
Perhaps there is no really good substitute in Australia?