Well, at least that's settled

The New York Times reports that the DPRK bomb was a plutonium weapon.

Test weapon powered by plutonium
The Australian

October 17, 2006 - US intelligence agencies have concluded that North Korea's nuclear test on October 9 was powered by plutonium, rather than enriched uranium, The New York Times reported today in its electronic edition.

The newspaper quoted officials who reviewed the results of atmospheric sampling from which a radioactive material was found. The sampling was collected after the blast, it said.

North Korea has obtained plutonium by reprocessing the spent nuclear fuel rods extracted from an experimental graphite-moderated nuclear reactor in Yongbyon, though exactly how much is unknown.

So the MTC laziness conjecture holds--and likely explains the low yield of the first test.

Plutonium - a snap to extract; an absolute pain to set off.

Uranium - an incredible pain to extract; a breeze to blow up.

A guess about the second test: while still nasty as all heck, a sub-1000 ton fizzle is insufficient as a deterrent. The DPRK has little choice but to continue testing until the ignition of a successful (10,000 ton or above) explosion.

Of course, given the DPRK's pathetic poverty and unreliable technology, the country may run out of plutonium cores before it manages to conduct a single successful test.

Couple this with the rather brief flight of the Taepodong II in July, it is safe to assume that Kim Jong-il is one really ticked off Supreme Leader...and the scientists and engineers of Punggyeyok are in a real hurry to conduct a second (and, they pray, successful) test.

Later - This post originally had the sizes of the nuclear explosions off by a factor of 1000. The correct numbers have been inserted.