You lose all of your Nephalem Valor if you change any skill, move to the next act, leave the game, or let the 30 minutes run out.
If you defeat an Elite or a group of Champions, not only does your Nephalos Valor go up a level (up to level 5), but the timer resets to 30 minutes.
So basicly, as long as you don't change your skills and you keep defeating those rare enemies, you'll keep a huge boost to your Magic & Gold find the entire act, getting better loot in general, but also from Act Bosses (very useful).
it makes the bosses drops better if you at level 60 and kill 5 elite packs before taking on the boss, on a 30 minute timer but it resets every time you kill a pack. (or just the guy with the name if its a guy + minions)
If the next one is called, because of his MO, the underwear bomber, you'll know I'm on to something. Calvin Trillin June 16, 2006.