The map at the article Camilla linked was quite illustrative: It purports to show the location of 150 "incidents" between North and South Korea since the "armistice" "ended" the conflict. A total of FOUR occurred someplace other than within South Koreas land borders (of those, all but one occurred in open sea). That said, I'm still not convinced a military strike is the next logical step, but we should break off diplomatic relations until/unless North Korea demontrates some significant and tangible concessions. Simply crawling to them for another agreement they can violate with impunity while they prepare for a war of their own choosing would be ridiculous. How many people do they have to kill before the US and her allies are no longer the aggressor? We're passed that point, IMHO, and it's time to draw a line in the sand and say the next time the next attack will be treated as the act of war it is and responded to accordingly.

Of course, that does mean some pretty awful things, things like North Korea shelling South Korea (because, remember, as long as we sit mutely taking this crap North Korea won't unleash an artillery barrage on South Korean civil--oh, wait, that's a proven load of horsecrap, isn't it? ) and the US confronting China, but it should be clear to any objective observer by now that that day is coming whatever we do.