There are indications out of North Korea that the long range rocket they've been planning to send into space is being dismantled due to technical problems, which explains the decision to push back the launch by at least a week. Satellite images appeared to show the three stage rocket being removed from its launch gantry, presumable so that it might be repaired and then re-installed.
It was revealed over the weekend that the North was expanding the window during which the test launch might happen, suggesting there would be delays, but actually breaking apart the rocket could mean more than a minor technical glitch or bad weather. Sources in the South have indicated that the launch is not canceled, but will eventually go ahead, if and when the problems can be sorted out. The last time North Korea tried to launch a rocket it was an embarrassing failure, so it's probably not worth any effort to rush it.
The delay also has the added benefit (for the North, at least) of pushing the launch closer to next month's national elections in South Korea and Japan. The launch was originally meant to mark the one-year anniversary of Kim Jong-Il's death, but any chance to put their regional rivals on edge in the middle of an election campaign is just an added bonus.