Just did a quick calculation to see how much armor pen a jungler like Nocturne would need for the new jungle, but I want to make sure I'm right!

Relevant Info:
Armor Pen Calculation: Armor Reduced = Target Armor * (1- Percent Pen) - Flat Pen

Masteries:
8% Armor Pen Mastery
+5 Armor Pen Mastery

Mob:
Lizard Elder 20 armor
Blue Golem: 20 armor

The following equation should give us the needed flat armor pen to bring a target with 20 armor (buff mobs) down to 0:

0 = 20 * (1-.08) - (5 + Flat Pen)

Flat Pen = 13.4

Is this right? I have a bad habit of mixing things up, so I need a double check!

I can't say if you're right, but I can tell you that with the changes, armor penetration has been cut in half, to 12, from 25, considering you run marks and quients. Either way, you won't have enough, so it's probably smarter just to spec them in damage instead, which will help your ganks and scaling on your abilities as well.

With the new Hunter's Machete true damage, Attack Speed is still far better.

Don't really worry about armor pen man. The trick is to just get your first clear done with, get in a gank, and then go back to base for your hunter's upgrade. Once you get it (preferably madred's) the jungle will melt like it used to in S2. The only major difference with this jungle is that it makes early invasions,counters, and ganks more difficult due to the jungler not only having to spend more time at camps, but he's generally lower on HP.

Stonewall008 did a noc S3 run through and states in his videos that you mainly need armor yellows. He leaves the other 3 rune choices up to preference. I've been doing this and been doing just fine.