Thats actually an excellent comparison - although in the US we use a different (non-intl unit) measurement system which is in millirem and rem (1000 mrem = 1 Rem)
the micro sieverts he uses on the map equate to our units of measurement by using 1 mrem = 10 micro sieverts
The legal limit the nuclear industry workers in the US are allowed per year is 5000 mrem, although none come even close - the highest Ive ever received in one year is around 2000 mrem.
The natural background we see in the US at sea level is about 310 mRem per year - 40 mRem comes from your own bones (potassium is radioactive) and another 310 mRem from the average xrays, medical and commercial/industrial operations(smoke detectors, exit signs above doors etc etc)
If you happen to live in Denver you obviously would get more since you are closer to the cosmic radiation coming in from space - and flying gets you a little more each flight.
A good read for the US background is:
http://www.nrc.gov/reading-rm/doc-co...radiation.html
The levels outside of the worst damaged plant in Japan is somewhere between 2 and 4 mRem per hour if you were standing at the fence constantly.
In comparison - the worst radiation levels anyone was exposed to at Three Mile Island was at the fence and it was 1 mRem per hour - at the height of the accident - and then tapered off to background levels after a few hours. Of course the only people close to the fence were the news media and they had to be shooed away to make sure they didnt get that extra 1 mRem since they aren't evidently capable of learning anything about nuclear power
