Nobody is taking this seriously in the press. The DPRK says crap like this all the time, its hard to tell if they are serious this time; it seems like they probably aren't. Now that could change as we get more information, but for now...its just the same-old-same-old. But us expats who live relatively near the DPRK (in the PRC or ROK) will always pay attention to stuff like this.
Well, if it is as you say, in a way it worries me more. Maybe they have declared all-out war in these terms before, I wouldn't know. In any case, if it isn't this time, for how long more? If nobody takes them seriously, the defenses will be lowered when they finally strike. I have little doubt NK is a country which could put all to risk because of it's dictator's crazy whims. It's a high risk the world is taking by dismissing it.
Everyone takes them seriously, just no one pays attention to what they say anymore, which is basically not useful information. We can only go by what they actually do.