There was a good analysis done by Slate, I think, about 9 months ago. Basically the gist was that Kim is the head, and looked upon as a god (actually, his dad is still leader/deity even though he's dead) but Kim can't run the whole place himself. Those who have responsibilities within the government also have some power and influence, such as leaders within the armed forces. These are the ones, the ones with diverging goals as well as personal desires for power and influence who also have the means to effect unrest.
Also, an article in China Daily
http://www.chinadaily.com.cn/ a year and a half ago described construction of a fence along the border with North Korea to "help with immigration control" was most telling in that it showed a section of large barbed wire imposing fence akin to parts of the fenced (rather than walled) old Berlin Wall. The gist of the article was all happy and friendly, but there are issues with many North Koreans trying to escape to China by crossing the river.
And as we all know, conditions for regular people within the country are not only opressive but horrible due to lack of resources and food.
I'll look for the exact stories I refer to above.