First, Our thoughts and minds are with all the citizens of Japan at this, their time of need.
As efforts are being coordinated around the world for relief as well as locally in Japan, the cloud can be used for mobilizing relief across the country and the globe. Relief agencies can share information, resources, and implementation plans quicker and faster using a shared model made available by the cloud. With the potential of traditional IT infrastructure being damaged or briefly immobilized, the cloud offers a solution to sharing and managing information as well.
One of the less touted, but equally important, advantages of cloud computing is more nimble disaster recovery and the potential for a quicker recovery time. In a sense, it provides more security as if one of your data centers suffers, you have a backup in other places.
I see the cloud playing a huge part in the mobilization of relief as well as helping rebuild and reform any lost infrastructure after this disaster.