You should really have a look at this very comprehensive and informative entry on MutantFrog.com:

There is an awful lot of panic and speculation regarding the situation at the Fukushima #1 (Daiichi) Nuclear Power Plant and in particular its possible effects on the Tokyo Metro area. What is really going on?

Short answer – things seem to be pretty safe for now, but there is still a possibility of danger if things don’t go well.

A nuclear scientist on MetaFilter mentioned the following, based on what is currently known.

… while I would certainly be keeping a close eye on the situation if I were in Tokyo (!), I would not yet be very worried about health effects (or finding concrete bunkers) given the information currently available.