This isn't the first time North Korea has done this. In 1998, North Korea fired the Taepodong 1 missile claiming that it had successfully launched a satellite into space. The first stage of the rocket fell into the Sea of Japan between the Korean Peninsula and Japan, and the second and/or third stage fell into the Pacific Ocean on the other side of Japan. (Unknown whether the third stage either failed and fell with the second stage or if it separated successfully and then fell at a different location.)
To perpetuate this unsubstantiated claim of a successful satellite launch, North Koreans gathered at their public square in Pyong y'ang once a month and looked upwards in celebration of their mythical satellite as it orbited overhead. (No other nation has been able to confirm that there was a satellite or that it ever successfully made it into space. Given the sophistication of modern detection systems, this should have been easily confirmed.)
What makes this North Korean act so significant is that the Taepodong missile, for all intents and purposes, is a WMD delivery system derived from a Soviet-style Scud rocket. The Scud is a tactical weapons delivery system. What that means in layman's terms is that it is designed for short range deliveries such as attacking the logistical bases of an opponent located in the rear area of the traditional battlefield. While theoretically possible to be used as a strategic weapons delivery system, Scuds tend to lose accuracy at longer ranges as proven during the first Gulf War. The North Koreans are claiming that they've developed a strategic weapons delivery system, and some analysts claim that the North Koreans have the capability to strike Alaska with the Taepodong. I personally believe that while the Taepodong may have the capability of traveling the distance, a missile aimed at Anchorage, for instance, may land on Anchorage or it may land in the East Siberian Sea or in the Artic Ocean or Gulf of Alaska. I doubt it can make the distance, but that's just my own personal opinion. This is like converting a Volkswagon into a Ferrari. While the dimensions of the frame are compatible, it takes more than just just modifying the chasis and installing a bigger engine to make it perform like a Ferrari.
The immediate concern is that the North Koreans have a definite capability to strike targets in South Korea and Japan. This is what all the hubbub is about.