What are the hidden effects of the nephalem valor buff?

The buff is explained in this question: How does the Nephalem Valor buff work?. It is said that there are hidden effects, and I'd like to know those.

From diablo.incgamers.com (Nephalem Valor > Magic Find... MF is Broken)

I used 140MF without NV buff and went to kill Zoltan Kull and he drop non of yellow in 10 games. When I have 0 MF and stack of Nephalem Valor (5) 75% mf I'm getting 1-3 yellow and 3-5 blues.

I experience the same effect: if I do siegebreaker runs with magic find gear switch, I am up to 130% mf, and I still have poorer loot that when I kill him with 5 stacks at 75% mf. So what are the hidden effects of the NV buff ?

This Blizzard Post on the upcoming patch Aptly describes the hidden benefit of the Nephalem Valor buff and the changes coming to it. (It's roughly 1/5th of the way down the post, "The Nephalem Difference")

Ahhhh screw it, here's the quote:

"It’s no secret that our goal for the end-game item hunt is players hunting monsters packs, building to five stacks of Nephalem Valor, and then killing a boss. While we’re seeing a lot of that occurring, what we’re missing is people feeling like it’s worthwhile to continue onward after killing a boss. To help hit that goal we’re lowering the number of guaranteed Rare items on bosses when you have your full five stacks of Nephalem Valor from two guaranteed Rares to one guaranteed Rare (you still have a very good chance at multiple rares, it's just no longer guaranteed). In exchange, all champion and rare packs will now drop a bonus guaranteed Rare item when you have your full five stacks of Nephalem Valor. The change benefits players with more overall drops, and a reason to push to continue progressing."

In addition to increasing your magic find and gold find by 15% per stack, Blizzard have confirmed that the Nephalem Valor buff will also increase the number of items that drop from elite/unique/superunique(boss) class enemies.

In version 1.0.2 (current at the time of writing) with a full five stacks of Nephalem Valor, you are guaranteed two rares from a "Boss" (superunique) kill in addition to greatly increasing the chance that others will drop due to the additional magic find bonus.

In version 1.0.3 (going live soon, announced by Blizzard here) this buff will be adjusted to only guarantee one rare drop from "Boss" (superunique) enemies in order to entice people to farm rare packs instead of bosses.