For once, I am actually in agreement with Meat Pie - its the USA I fear the most on this planet, not Iran, N Korea or China.
You need to ask yourself why are these countries building these armaggedon weapons in the first place? Take Iran for example, vast oil reserves, doesnt want to bow down to the USA and its allies, gets threatened with attack, so in response it builds nuclear weapons.
Also, with the state of the world at the moment, i'd be more worried about Syria than N Korea. I think things will flare up in Syria way before N Korea which will drag in the rest of us, and thus commencing WW3. Its already started - Isreal has attacked Syria last week, Iran has vowed revenge - Iran then attacks Isreal, Isreal attack Iran, USA gets involved as its Isreal's ally and is dying for any excuse to attack Iran, then Russia and China step in to protect Iran and Syria.
Iran nukes Isreal, Isreal nukes Iran, Russia and China get to a nuclear standoff - all very possible and all very possible within the next few months!!!!!
So in answer to the original question - no, im not at all worried about N Korea! lol. Just wish the USA could keep its nose (and weapons) out of other peoples business (and countries)!