As an Aussie, I feel qualified to make a statement here. Now, I'm not racist against US Americans; I love me some US citizens! To be completely honest, actually, I think pretty much everyone in Australia thinks the actual *people* of the US are okay.
What actually pisses us off about the USA is that the government is so...arrogant! You've got all these guns, you spend billions of dollars on your military every year, and so you've got swagger. President Bush seemed like a right old moron; that made your government seem like a bunch of morons. Your wars in Korea, Vietnam, Iraq, Afghanistan, all seem like failures. Your government's justification for these wars - "A war on terror/Communism" - seems like a load of crap and paints your country as the world's policeman. Yet you can't win your wars...hm.
Your government is spending billions on the military and neglecting healthcare and education to maintain its position as the world's policeman. Here in Australia, you don't have to pay to go to the doctor - the government pays most of the bill for you. This means that anyone can see a doctor anytime. When Obama tried to introduce such a bill in the US, he got shouted down because it's apparently fiscally irresponsible to take care of your citizens. Now from an Aussie point of view, that seems like a load of rubbish, so the collective question here is, "Why the fuck are you spending billions on the defence force when you could be making a country full of intelligent, happy, and healthy people?" And our collective answer on your behalf is "Because your government is full of arrogant pricks who want to control other countries through force and military might."
There are a few other, smaller issues I could mention, but really, that's the crux of the matter - that your government comes across as stupid, ignorant, power-hungry, and arrogant. Couple that with the stereotypical image of a millionaire Texan with a big gun and a brain the size of a pea, and that's what half your Congress seems to be from an outsider's perspective.
Now, before you all hate on me - this stuff isn't necessarily true, it's just the way it seems from outside. In the same way that water seems shallower from above, and you don't actually understand how deep it is till you get in, our view of your country is almost definitely shallower than the view of an American citizen. So to reiterate - this is just public opinion from an outsider's perspective.
In regards to the American people proper, most Aussies think you're okay. We recognise there are some wackjobs - Charles Manson, the Westboro Church, the guys who bomb abortion clinics, rednecks - but every country has dickheads. Most Australians think that Americans are alright. In my personal experience, I've met a few US wackjobs - rednecks, fundamentalists - but the vast majority of my US friends and acquaintances are alright. At the very least, the US people here on SC seem okay to me.