Fukushima's most important lesson is this: Probability theory (that disaster is unlikely) failed us. If you have made assumptions, you are not prepared. Nuclear power plants should have multiple, reliable ways to cool reactors. Any nuclear plant that doesn't heed this lesson is inviting disaster.
Should we be concerned? A nuclear official said in passing this weekend that problems in 14 areas need to be resolved. In the wake of Fukushima, a shade more transparency would be welcome.