Basically, my idea is that I'll stop losing weight when I have to use drastic or unhealthy methods to keep losing weight. So when I reach a point where getting any more weight off involves lots of hunger or too much exercise then I'll stop there.

BTW, I would define lots of hunger as the kind of dieting where I'm obsessed with food all day, feel cranky, have physical hunger pains etc... IOW, the way I used to think that being on a diet had to feel. And too much exercise is both when I don't give my body a chance to recover and when feeling obligated to exercise outweighs my enjoyment of movement.