sandman: the blackbody shader is really useful when you want to eliminate that blue tint your interiors are given from a daylight/sky portal combination
set the scene up the same as you would normally for an interior with daylight and portal, then assign the b.body shader to the portal and change the kelvin to the same value that you have set for your white balance in your exposure control and voila you have a white room rather than and blue tinted one, or just play with the kelvin temp to get different coloured tints, comes in very handy when customers don't like the 'real world' blue tint that you get as standard.
(thanks to jeff.p for letting me see the light with that one)