I visited Seoul when I was pregnant with DS, and I really loved it and the people there.
I'm worried. I'm not worried that they can reach us here, because they can't. The problem is the knock-on effect, will China help them? Even China (according to articles I've kept up with in the Economist over the last year or more) has been trying to distance themselves a little bit from some of the crazier declarations NK has made.
The US will help, they will have to help, Korea is our ally (sorry, am American hence the 'our'). We have bases there, we were integral to the rebuilding effort after the war and haven't really 'left'. We have very close relations with their government.
China has been one of the few countries to aid NK. What will they do? I don't know. China shouldn't want a war with the US. Economically, they are producers, and we are consumers. It would have a massive knock-on effect on everything they've achieved over the last 20 or more years. The two countries have a massive trade imbalance, in China's favour. They own a lot of American currency as well as stocks of ours.
But they could, if they wanted to. There's only one country in the world that spends more money on their military than the US, and that's China. And this particular Chinese government is very military-orientated.
The thing about nuclear weapons is they are a great deterrent. Everyone has one; no one wants someone crazy who doesn't care anymore going and using one. The problem with NK is (imo) they are getting close to having nothing to lose. The people are very, very poor, starving and beaten down. If he decides to take them all down in a blaze of glory by starting WW3, he could. NK doesn't have economic incentives not to do it (unlike the Chinese one I touched on above). They've had sanctions against them for ages and have no real trade outside of China and a few others.
I'm babbling. I could seriously go on about this for ages. :)