I'd definitely support it. The fact that North Korea still exists is a blight on mankind, so far as I'm concerned, and the faster that regime is toppled the happier the world will be for it, I say. There are few military actions that would be more justified, assuming it were provoked. And even if it weren't, I wouldn't lose sleep over it.
It wouldn't be hard either. North Korea may have a large military, but it is poorly trained, ill-equipped, and half-starved. Conventional victory would likely occur within a matter of months. The biggest concern would be the fate of South Korea in the early months, considering North Korean artillery, but if that can be disabled quickly (I imagine that would be the first target) then we'll have little to be worried about.
I think people in this thread are seriously overestimating how willing China would be to intervene on the North's side. The only reason they support them at all is because they'd rather not have refugees swarming into their country, but that isn't something they'd go to war over, particularly when it puts their economy and relations with the US (and the future, reunified Korea) at risk. They're fine with keeping the status quo, but they're not willing to die for it.
People seem to be comparing this to "another Iraq" as well. There's not really a comparison between the two. North Korea has no ethnic strife, no tribal conflicts, no regional divides or factional infighting between tightly-knit groups, and no method of foreign terrorist insurgents from taking root, either. The US wouldn't need to create a new government from scratch, it would be a reunification led by the South - a difficult and expensive process, but not an impossible one. A full-blown guerrilla resistance seems unlikely, considering that the ordinary people will likely lose sympathy with their former masters once they've fallen. Think the occupation of Japan or Nazi Germany, not Iraq.
And really, it would be an entirely just cause. North Korea is an abomination, and we would all be well rid of it. Sitting back and waiting is not going to make things any better there, so why wait? It would be preferable if it were an international coalition organized within the UN, but even if the US had to go alone (though the South would still probably be doing most of the work), I wouldn't have any reason to object.