The first that comes to mind is the fact that a technologically highly developed society witnessed this disaster. This means that the quake, the tsunami and the nuclear disaster have all been recorded both with amateur equipment like mobile phone camera's and by sophisticated specialist equipment. In 2004 much of the tsunami data was recorded once the water had receded. There is much more 'live' data coming out of this disaster that will teach us much more about the behaviour of shock waves, large bodies of water on the move and dispersal of radio active material once it escapes the reactor. In short: data becomes knowledge. Knowledge aids prevention and management of disasters.
The nuclear disaster at the Fukushima nuclear power plant shows us that our lust for electricity has us use technology that we can not contain as soon as things go wrong. Nuclear disasters are rare but once they do happen their impact is big.
It will be impossible to suddenly close every nuclear energy plant in the world. Eco-warriors may shout for that scenario but the electricity they use to power there bullhorns must come from somewhere. There are too many of us that plug in too many devices on a daily basis and nuclear power is too cheap, too plentiful and statistically too safe not to use it. But, and it is a big but, we have now seen again that a nuclear reactor starts to live a life of its own once we lose control over the system. The Chernobyl disaster was also such an event and Three Mile Island in the US, although the effects were minimal, another. The costs of such a disaster are tremendous and make the argument for cheap energy a tenuous one.
So the disaster in Japan may make us think again. It may stimulate companies and governments to start investing into the development of alternative energy sources in a big way. And the alternatives are there. Apart from solar, wind and wave energy, there is the TWR (Travelling Wave Reactor) which uses depleted uranium as its fuel. In one process we have zero emission energy and we get rid of our nuclear waste. Sounds too good to be true? Only further research will tell but in my opinion it's worth a shot! A disaster like this may open doors previously closed. Investment both in time and money and a willingness to listen to alternative energy proposals may become more readily available now that we have been faced with a nuclear disaster in a modern, technologically highly developed country.
Another, more sinister aspect of the nuclear disaster is that there are relatively few nuclear accidents on this scale. Data coming from a real world situation is always more valuable than data coming from a simulation. You can test fly a plane but you can't test fly a nuclear power plant. This accident will teach engineers a lot about the process of an accident and it will help make future power plants safer. Because, until we have found an alternative, new power plants will have to be built. Unless we substantially change our ways.
The Japanese people have shown themselves as examples to most of the rest of the world. A disaster like this could have easily sparked widespread looting and food hoarding in most other cultures. Not in Japan. The calm and reserved way they are dealing with this disaster is exemplary. There is an interesting article and discussion on this subject here: http://aidwatchers.com/2011/03/why-no-looting-in-japan/. Researchers into human behaviour and the mechanics of society may learn a lot from the way the Japanese people are coping with this disaster. This may teach us all something valuable in a world that is becoming more and more crowded.