According to Russian intelligence the weapons are extremely bulky. I'm not worried about NK's weapons falling into the wrong hands either. After all that effort they can't allow that to happen. In that sense Pakistan poses a far greater threat. One coup and you're done.
As for NK's willingness to use them, i doubt that is even the point. NK was in a state of MAD already and that hasn't changed. The nuke secures Kim Jong-Il's position. The primary objective of all dictators is to stay in power.
The bomb's yield is reported to be around 20kt, similar to hiroshima. The nuclear test has NOT been confirmed by seismic readings yet.
Edit: I'm reading here there has been an explosion, in the order of .5 - 10kt. It cannot be confirmed that it is nuclear, atmospheric research can confirm that later even for underground tests (some gases will escape), but it is also possible to conduct a test in such a way that it is impossible to tell whether the explosion is nuclear or not. A few thousand tons of convenctional explosives are a lot but not impossible to make.
It wouldn't be the first time NK bluffs.