With lev 60 after defeating a champions group or a rare monster you get the Nephalem Valor Buff.
The buff increase your magic find and gold find for 15%.
The buff stacks 5 times, this means 75% magic find and 75% gold find.
The buff lasts 30 minutes.
The duration resets to 30 minutes with each kill of an elite pack.
The buff ends if you change skills.
You get the buff in all difficulties, also normal and nightmare.
With this buff you get additional item drops if you kill a boss like skeleton king. (This is not 100% confirmed now!)
There are many possibilities with this buff, which must be discovered now.