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In the year 2010 this must still be managed by the application (distributed processing where chunks of work are distributed and the results are put together again, like SETI). An OS is not capable to do this, even with virtualization.
Well, actually, 20 years ago Groupe Bull had an OS that did precisely that. 
It allowed a single OS image to span entire networks and use resources as if it were a single computer. But I agree that no mainstream OS provides the functionality.