First off, there are two distinct sites that are owned by Tokyo Electric Power Company TEPCO in the Fukushima Prefecture. Fukushima Daiichi (literally One) and Daiini (Two):
Daiichi is the home to six separate reactor cores while Daiini has four. Currently, the reactors in question are units 1 and 3 of Daiichi. Unit 1 is a General Electric BWR/3 design while Unit 3 is a BWR/4 design. The major difference is an increased power density of 264 MWe (Mega Watts electric).
Japanese power plants take advantage of using the ocean as their natural heat sink. All power plants require a large supply of water to disperse unusable heat. Typically either the ocean, a lake, river or a picturesque cooling tower is used for this purpose.
At a glance, a nuclear power plant is similar in many ways to its fossil fuel cousins. A heat source, whether it be the burning of coal, oil, natural gas or the fissions of uranium from a nuclear plant, provide energy to increase the temperature of water.
The energy density though of uranium is orders of magnitude higher than any fossil fuels. This means that a few tons of fuel material (uranium dioxide and zirconium cladding) can supply the same amount of energy as massive heaps of coal.
The concept is not unlike that of a pressure cooker in yours grandmother's kitchen. We can use the pressure differential of the built up steam to turn the blades of a turbine. This turbine is connected by a huge shaft to a generator; basically a massive rotating magnet. Using good ole' Faraday's Law we can induce a movement of electrons which is currently powering that glowing box you are staring into.
One, a great many of the ~12,000 or so fuel rods would have to be pretty fully uncovered for a decent amount of time before getting up to the 5189 degrees Fahrenheit needed to begin to melt. Even then, it would need to become a molten ball of what is called 'corium' that then slumps to the bottom of the pressure vessel. This massive structure would then dissipate a tremendous amount of heat due to conduction with the molten fuel. A typical pressure vessel is around eight inches thick made of steel with an outer liner on top of that. Just think about that. That is a lot of steel to go through. Even if it gets that far, it then gets to dissipate its heat through the pedestal and eventually the concrete base-mat that's around 20 feet thick (to stabilize against earthquakes mind you).
On top of that, there are multiple systems within containment that are designed to keep the gaseous fission products in. There are series of HEPA and charcoal filters that catch quite a bit.
On top of that, there are perimeters established at nuclear facilities to keep the public at a safe distance in case of a release. On top of that, the Japanese government has take the precaution of moving everyone a LONG ways away.
The bottom line:
Is this a significant occurrence: yes; one I will certainly always remember in my career.
Is there going to be a catastrophic event where the deaths of many people are involved with the nuclear facilities: there is a finite probability that tends to nil.
Should the news agencies be focusing on the reactors instead of other events: no, let the engineers do their job and we will let the journalists do theirs.
Should the engineers keep everyone informed: yes, and they are but with the internet media these days its a little hard to find Waldo (TEPCO, NEI, IAEA) in this sea of ramblings and misinformation.