Nephelem Valor

[Sid]

5 stacks = +75% MF and +75% GF.

The duration of the buff is 30 minutes.

Every time you kill a rare or champion pack the duration resets back to 30 minutes. Killing a boss does not reset the duration (but does not cause the buff to expire).

The buff is persistent through death, but not from one game to another.

[Toetag]

If you open up your inventory, then click the details button, you'll see your current MF all the way at the bottom.
That number will include your MF from gear plus the increase from nephalem valor.
As you gain stacks you'll see that number increase.

Didn't think of that. Thank you for the tip and to all the replied.