Well this isn't your all-standard nocturne guide. I personally use the ult for chasing out single targets. I never blindly focus the ad carry. Often times the ap carry has more burst then the ad carry damage over a whole teamfight. ADCs nowadays just run away again, leaving you killed by the AP carry, jungler and toplaner. You need to check their items and so on and decide which target will be the best. Also if the adc made 0 kills and 0 assist since respawning and the apc made 3 kills, would you still target the adc? I clearly wouldn't. And just building defensively because of one skills is kinda weird. Show me one full tank Katarina! Katarina gets focused all the time, because she could always jump in and triple kill with her ult.

And again, this is a NOCTURNE guide, not a LEAGUE OF LEGENDS guide.
Also there is a todo-list at the end => guide is not 100% complete yet.

I think it is not really necessary to have a huge rundown of summoners. Its nice to have but it seriously isnt a must.

This is a guide -.- Everything need to be explained, I don't care the hell what you know and don't.

As nocturne you will be diving in the enemy team - by diving in the enemy team you will automatically be caught by all the enemy AoE and you will be the focus of the ad carry because you will jump on him

not enough defense = dead.

Let's break it down to some goodies and baddies:

Thy sins
1. No comment to vote
2. Spelling mistake in cheatsheet
3. Your cons are pretty bad.
4. @rune explanation; fun and all to see what they do, but why are they better than other runes (explain it in your guide, not here!)
5. Same with summoner spells
6. "(instead of Flash) Show me one Nocturne that uses Q and ghost and still needs a gap closer. Hecarim would love to have that much movement speed :P" I am not sure if this is an argument why Nocturne shouldn't take it, or an argument that Nocturne should take it.
7. For the love of god, explain your choices better! :S 1 or 2 sentences is not enough to explain every single thing.
8. No tactics section

Thy blessing
1. Though the jungle build is a bit squishy, the build overal is decent.
2. Well structured cheatsheet
3. Good use of coding
4. Good use of structure

Result: Path of Redemption
Your laziness (or lack of explanation skillz) hurts your guide a lot.
You need to explain your choices a bit more in-depth.

Overal, your structure + cheatsheet was fine, so there might still be hope for you :P
At any rate, keep working!

Have fun :D

What does he mean so offensively?

Runes we've got armour, magic res and move speed..

starting with 5 pots for sustain

then very early he's buying health and mercurys treads..

more health.. a brilliant cheap offensive item.

then yet more health with a frozen mallet coming up too, a few tier 3 offenive items later on in the build

then lots of defensive options to choose for final items

maxing his defensive skill second..

9/21/0 etc. etc..

What can I say more about basic items, that only matter in the early minutes of the game? And the summoner spells are pretty obvious and basic knowledge that everyone should have.

The summoner spells and starting items must be explained better

Because he after all is not a tank. Armor Penetration in combination with attack speed are his huge stats. And looking at the items, there are at least 2 defensive ones. If you really want to go more tanky, you could take out Last Whisper maybe and take a second item from the "last 6th" category.

Why would you EVER build nocturne so offensively?