The shuttles that NASA uses to fly to space currently use measurements in the form of pounds and feet as opposed to the more widely adopted meters and newtons. The upcoming shuttle replacement will continue to use the imperial measurement system because it would cost NASA $370 million dollars to convert to the "'International System' of units".
In 2009 a launch to put a shuttle into orbit costs approximately $759 million dollars and to spend half the budget of a launch to convert units of measure can not be justified because it will produce no gain for the agency or the shuttle occupants.
To convert to a new system of measurement is not as easy as it sounds. NASA has formulas crafted in Excel that are thousands of lines long that are able to give measurement and predictions in almost any type of circumstance. Changing such formulas and re-verifying their accuracy is a long timely process that no one at NASA wants to undertake.
NASA's Constellation program will replace the aging shuttle in the next decade but an exact timeframe has not been set as the testing of a new rocket system will take years to perfect in order to give our astronauts the safest possible journey to the heavens above.