yeah. you may not use that full 1000W. Then what is the use.
600W is more than enough for today's hardware unless you pick four SLI cards
Moreover, all these h/w companies are trying a lot to bring down the wattage of their products.
If you take Nehalem/Phenom/HD48xx series/9xxx series. They are lot better than yester years hardware.
Even for 8800GT, a 500W power supply is enough. IN that case, why is the need to go for 1000W SMPS, just because it is 100W???
PS: if you want to use 1000W SMPS, get a cabinet that can hold this coz those weigh around 5kg and most of them come with extra fan at the top.