I am as much a hawk as anybody. However, I am nervous too about this pre-emptive stuff against non-states. There are two nuances to it. The first is the way the US is actually conducting its war on terror: Once the US identifies a terror cell in a foreign country, they are coordinating with the foreign country for either them taking care of the problem, or we take care of the problem after coordinating with them.
The second way of doing it is the way most people would characterize the Australian prime minister's words: Australia would deal with the problem with no coordination with the relevant nation, thus violating its sovereignty. That's the way the Europeans are mischaracterizing the US response. This sort of policy would give tyrants a great pretext to invade neighbouring countries (such as the Russians inserting themselves into Georgia, regardless of the willingness and ability of Georgians of dealing with the terrorist problem themselves).
Pre-emptive strikes are justifiable in a host country that is unwilling or unable to act in coordination with the threatened country to eliminate the threat. One would hope that a country that is merely unable to act on its own initiative would be willing to cooperate, of course.
But this is merely an extension of the doctrine of striking at terrorists and those who harbor them. In most cases, it is not a strike at the host government, but where that is necessary, I don't have a problem with it.
The nature of warfare has changed in the past 100 years. In the past, aggression would manifest itself as an invasion across an international boundary or on the high seas. Today, weapons of mass destruction can be launched from within a country against another without an invasion, or infiltrators can instigate attacks in a neighboring country using the element of surprise. We call those infiltrators "terrorists."
It is unreasonable for a country to have to absorb a blow before acting against a particular threat, especially when those responsible can simply disappear into a civilian population after an attack. The only means to protect against such attacks is to destroy the people who are planning them wherever they may be.