The reactor damage in Japan has progressed beyond the point at which only noble gases and iodine are released. Cesium-137 releases have been detected. This is a sign that the fuel has been badly damaged. I am hoping that the containment will be able to prevent the majority of the cesium escaping from the reactor site.
The good news is that the wind is blowing the majority of the radioactivity west away from Japan and the mainland of south east asia.
The other good bit of news to bear in mind is that no steam explosions have occurred at the reactor site, the only explosions so far have been hydrogen / air explosions which occurred outside the containment which are less damaging to the containment than a steam explosion inside the containment.
Some steam explosions can take the form of a BLEVE, this is a much more nasty explosion. A boiler which suddenly bursts when it contains water heated above degrees centigrade can give a BLEVE.
As the reactors are no longer critical and have been cooling for over a week I think that the chance of a steam explosion is now very small. The horror explosion at Chernobyl was a steam explosion which progressed to a hydrogen / air blast, the heat source which drove the Chernobyl blast was a sudden spike in the nuclear reaction rate in the reactor. Such a sudden heating will not occur now in the Japanese reactors.
Below is a link to a film which explains how a BLEVE occurs when a propane tank is heated in a fire. While the propane BLEVE will be followed by a large fuel air explosion a steam explosion in a reactor accident will not release nearly as much flammable matter as the majority of the liquid / vapour in the reactor is water not propane.
If you want to look at a film about a small reactivity induced steam explosion in a power reactor then I would suggest you view the following film on youtube.