White box on my power cord gets VERY hot?

Heat is kind of subjective. One persons 'hot' might be another persons 'warm'. With that said, mine gets very warm. Not too warm for me to hold though. I was actually thinking about getting a stick-on aquarium thermometer to see how hot it actually gets.

If it's really too hot to touch, maybe a call to Apple is in order.

The powerbrick only gets hot when it recharges the MacBook - touch it when your Mac has been recharged for a while and it should be cool to touch.

I noticed this too, and in addition, makes a kind of hissing sound when charging. I found that by attaching the charger to the extention cord rather than plugging it straight into a wall socket and then laying flat on the floor helps to cool it down. I think that by doing this the heat dissipates from the charger more easily. I have marble floors so that helps, it probably does't work so well on carpets.

I THINK (but I'm not sure) I heard that Apple will replace the hissing ones. You should look into it more.

If the heat in the power brick is becoming an issue, consider purchasing a replacement. They can, and do get hot. But if they get hot enough to actually cause a burn, that is when I would get concerned.