I sign up for all of them. All being the ones I find on united.com and on the 1Konly webpage.

And I never got any of the US targeted goodies. But they always either wrote me or did call me and offered me to give me some other bonus thingie instead. The Australian promotions are generally no match for the US ones so it's better to get something out of it rather than nothing at all.

On a related matter - they are quite flexible when you negotiate with them. Years ago I signed up for a promo where you had to fly 2x into the US to get some bonus miles. I flew SYD-SFO-FRA return and then asked for the bonus. They were arguing that this is a single itinerary, and I claimed that it does not say that in the promo. They actually gave in but told me that this would be a one off thing.
I love United, try to do that with LH or QF!