Chernobyl is about the worst that could happen. Tokyo itself would be unlikely to be badly affected even in a worst case scenario, but in Chernobyl the zone of long term radiation was approximately 60km radius.

Japan is also lucky that the nuclear disaster is occuring on the east coast, most of the fallout should be blown out over the pacific where nobody actually lives. Any radiation reaching the states would be pretty dispersed from what I've heard.

Of course as far as we know so far it's only a partial meltdown, nothing too bad (or permanent) will occur unless the fuel melts through the containment,

The news report I saw said that the winds at the time of the report would blow the radiation right over Tokyo. They said it wouldn't be as bad as the immediate areas but could cause defects and such. But they also did say the winds could blow it out over the ocean which is best case scenerio. But either way this would be very bad for Japan, even if they lost only 60Km of their land becoming unusable for along time, that alone is a large hunk of Japan. The loss would be catastropic.

I wonder if Japan has put measures in place incase the after shocks breach anymore plants? I'm sure they are taking tons of precautionary messures. Not to mention Japan is reliant on Nuclear power to run the country, they have to ensure their reactors are safe.