Not to intrude between Brennen.exe's and Zik's argument but I'd like to repost something from the 516 spoiler chap regarding Haki.
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Here is my take on the whole 'Haki' issue.
I think most of you are overreacting regarding the matter. I think that in reality Haki will become somewhat of a staple in the New World but you guys are overestimating the power you acquire by being able to use this technique.
The whole making-people-fall-to-the-floor-with-foaming-mouths has only been displayed by Shanks (one of the Four Pirate Emperors) and Rayleigh (the first mate of the Pirate Fucking King). Of course these people have incredible ambitions and would be able to project a sense or aura which would be more powerful the anything a fodder pirate can muster.
Aokiji, Kikzru and Sentoumaru as well as Kuma, Moria etc... have proven to be incredibly powerful and I am sure that to a certain extent the do in fact know how to use Haki. But that doesn't mean they can use it to the extent that the aforementioned guys can.
In general the StrawHats have been pretty weak in information regarding what's going on in the world (obviously for storytelling purposes). They didn't know about log poses, Grand Line navigation, Shichibukai, Admirals, EL, CP1-CP8. They are pretty naive in this world and that is how it always is with the main characters because if they know everything then the story cannot be told. Hell they hadn't even heard of any other Supernovae whereas all the others seemed to know/have heard of each other. So it makes sense that Haki has been around/being used without them knowing.
While Naruto/DBZ/etc chose to base the manga on such techniques, One Piece developed the characters, other crews and then decided to introduce the whole 'chi' idea at a later stage.
In the same fashion that SSJ/Sharingan would be an analogy to Luffy's Gears (hard to sustain, possibly dangerous at first, but then a relatively common and staple technique (which will happen with Luffy's Gears)), hake is really an easy thing to map an analogy to. Instead of using the obvious Chi/Over 9000 analogy I'm going to compare Haki to skateboarding. The numbers used below are only for educational purposes and probably aren't accurate, but they give a pretty clear picture.
50% of people don't skate at all.
10% of people have skated at some point but don't do it regularly.
40% of people can skate properly.
Out of the 40% skaters:
80% can skate from point A to point B as a method of stress release or maybe to get somewhere easier.
15% enjoy trying tricks in skate parks/half pipes etc...
5.9999999996268656716417910447761% can perform tricks in a fairly professional level.
0.000000000373134328358208955224% is Tony Hawk.
I don't skate but you see my point. Only one person in the world is Tony Hawk. Sure many people have used Haki but only very, very few are powerful enough to be impressive.