Nvidia 480 Series... This doesn't add up....

A GTX480 won't use more than 30A on the 12v unless overclocked nicely. The 42A thing is because you'd need some room for the CPU to run too. A GTX480 and a Phenom II/i7 won't exceed 42A.

On that, each rail is distributed. One rail can fuel the card, while the other fuels the CPU. Basically it can give each card 38A, instead of having to share with the CPU (which will get its own 38A).
 
The key number you want to look at when choosing a PSU is the combined 12V rail amperage. Unfortunately, that is rarely given in the specs (only on the label). However, newegg often takes a picture of the label. Just find the combined 12V wattage and divide by 12(V). You will get an amperage much greater than 42 amps.