First off, I apologize for being somewhat abrasive in my posts.
That being said, I'm still seeing "bean counting" in the assessments of people here (couchcommander, I'll address your issues of terrain below). Does anyone remember the gloom and doom of commentators about the first Iraq war? We were up against the world's fourth largest army. Thousands of tanks, hundreds of combat aircraft.
To risk cliché and quote Napoleon: "The moral is to the physical as three is to one." Perhaps it's our usual regard for the "inscrutable oriental" that we automatically assume the NK military is both technically capable and highly motivated. True, they are a highly propagandized force, with skillful indoctrination. However, the country is a shambles, with people eating grass. The military's primary motivation (at this time, my assessement) is that they are fed. If they are successful, they may well retain their motivation, by the factors I see point to a brittle force that will not be able to sustain much hardship. Their airforce and air defence forces are old, and more a means for US and Allied pilots to rack up kills than a credible capability. They are firmly planted in Soviet-style "top down" leadership, causing a lack of flexibility.
If they have any credible capability it's their SF, which has proven to be very well motivated and somewhat capable. They could easily cause difficulty in Allied rear areas, though those difficulties are not likely to be war winners.
Now, terrain. "Mountainous" is an oft-used description, but the Korean mountains are not the Rockies or the Alps. Look to the history of the Korean war and you'll see that it became a "battle of ridges" once the Allied forces left the roads. Massed armoured battles are not likely to be occurring there, but even in the days of the great Red menace in Europe armour battles would not have been Kursk or Iraq-like. Armour in Korea would be more effective and less vulnerable in the Korean terrain than it is in the urban terrain of Iraq today.
As for foliage and cover, couchcommander, you are right, much like the Eastern US, though the cover is much less now, as NK has been deforesting considerably in the past 10 years - the famine and lack of infrastructure means trees are fuel and food. However, the Eastern US is also quite developed. Korea is as well, which means things aren't as close as you may think. Yes, there will be defiles that armour may have to go through, but there were such things in Europe as well, and we trained for that. In terms of communications and vulnerability, it's clear advantage US. The NKs technology is likely more a restriction to them than to the US - the latter have satellites and air power far more capable than anything NK can cobble together.
A bloodbath? Probably, though most of the blood shed would be NK. This is not Iraq, either. There are millions of SK people who can, and would, provide propaganda value, translators, spies, SF and a variety of other functions that would reduce the US/Allied force's vulnerability to NK subversion, espionage, counter-intelligence.
Finally, it appears to me that most of the theories are predicated on a US/Allied attack. Such a scenario is pretty doubtful for a variety of reasons (like, it's been over 50 years already, why now?)
I ask that those who stand up with glib "it'll be a bloodbath" statements look at things in more detail. The number of factors that need to be taken into account are far greater than many of you seem to think, and the one most often missed is "the moral."
Anyway, I will now sign off.