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I'd say link to One Manga, but that's almost obsolete, just state or link somewhere else to the first chap where you downloaded a raw, read a spoiler, the one from where all the weeks of waiting followed.
Here was mine.
http://view.thespectrum.net/series/one-piece-volume-01.html?ch=Volume+32&page=119
Mine was
http://view.thespectrum.net/series/one-piece-volume-01.html?ch=Volume+35&page=147
I decided to catch up after someone spoiled me Luffy vs Usopp.
Chapter 489: The Eighth.
I watched the anime for a little bit before that, so I knew who Brook was before seeing him join. Still one of my favorite chapters.
I believe it was somewhere between 423-427: somewhere towards the end of the Lucci battle.
3DS FC: 0662-3589-2887
NNID: Gibbs-free
This is mine:
http://read.mangashare.com/One-Piece/chapter-572/page001.html
Kinda late to One Piece Manga… Yeah, shame on me
Can't remember what number but it was "Hunger Hell"
One piece practically had disappeared where I came from, so i would check it once a year. Then we got the Skypeia funimation arc in Australia and i got into it like that.
Chapter 525, the beginning of Impel Down.
I used to be anime-only, but after the Thriller Bark arc ended, I got all caught up with the manga after somebody spoiled the identity of the seventh Warlord.
http://view.thespectrum.net/series/one-piece-volume-01.html?ch=Volume+44&page=41
it was either this chapter or the one before it.
My first weekly chapter was somewhere around Usopp vs. Perona.
My first weekly One Piece episode was somewhere in the Ice Hunter filler.
Though I had watched the majority of the series before then.
Franky Vs. Fukurou
Chapter 564 (?): Luffy VS Mihawk
I knew of OP before via the 4Kids Dub, but a chance of hearing about it borught me back after all those years.
Ah…Think my first real taste was sometime during Enies Lobby.
I watched the Anime on German television, it stopped going further just before Kizaro arrived on SA (OMG) and since I could not wait months for it to continue I started watching the sub episodes on the net and just about a few months ago I catched up to it and couldnt wait a week for a episode so I started reading the manga until I catched up to it too and started waiting for a chapter every week.
580: End of war - the 1. one I waited for (^_^)
I think it was during the Skypiea Arc. Just finish catching up with the anime and I felt it wasn't enough.
http://view.thespectrum.net/series/one-piece-volume-01.html?ch=Volume+42&page=110
I'm pretty sure it was 406.
To help me remember my first chapter I looked in the archives and browsed the old chapter threads. It was nostalgic. I remember coming up with my user name because that was when I first read about the perfect clima-tact and thought it was named ultimate clima-tact for reasons I can't remember. I also came up with some bad threads when I first joined along with some bad posts and way off theories. I think I've matured in the past 4 years. Maybe.
Originally Posted by Nightwing
Stay focused, cause right now you have a decision to make. Are you a man perpetually looking back at what he’s lost, or a man looking forward, to what he might become?
Ch 316 I believe
http://www.onemanga.com/One_Piece/482/01/
i cudnt w8 for next week's episode so i start reading the manga 
Around 410 or so, it was roughly at Nami v. Califa.
Chapter 582, the one that started the Luffy, Ace, and Sabo flashback.
Obviously I was interested in the anime long before that. I got caught up to the manga because I was sick of getting spoiled.
My first weekly chapter was Chapter 440: Fire Fist vs Blackbeard.
Whatever chapter (masked) Duval's first appearence was
I had followed the anime for a couple years, but I got fed up with it during the Thriller Bark arc. (That episode where Zoro fought Kuma was just really really really bad)
So I started reading the manga and ended up a couple chapters into Amazon Lilly.
chapter 442 I finally caught up, right as Thriller Bark began and the scanlation image quality tanked
yo, visit me at www.agent-oharah.deviantart.com
I'm 80% sure my first chapter (at least when I started following spoilers) was chap. 451, a few chapters into Thriller Bark.
Was just finishing my Jojo's Bizarre Adventure kick (SBR wasn't translated at that fast of a pace), and I needed a new series. Heard so much about One Piece, but never read it before.
My first weekly chapter was, I'm pretty sure, Chapter 545, on OneManga obviously (it was the newest chapter)….
...had no fuckin' clue what was going on, so I figured starting from chapter 1 was a smarter way to get into the series....
I started at chapter 1, but when I caught up, it was a little after the beginning of Impel Down.
http://www.mangareader.net/103-2541-1/one-piece/chapter-434.html
I started just before Thriller Bark, I also watched the anime mainly and jumped to the Manga.
Don't know the number but the title is "Luffy & Whitebeard" (or the other way around, who cares). I found out about One Piece when the anime came out in America and I stayed with it all the way up to the end of the Alabasta arc before Robin joined when they stopped airing it. Since I didn't know what manga was or have a computer at the ready, I stopped following it for about two years and then started looking it up again. When I saw all the information about Thriller Bark, Impel Down, and all the new members post-Chopper, I had a fan attack and started wanting to follow it again.
One Piece ended up being my second manga after I finished Bleach and boy, I have to say that the transition was the greatest and most satisfying breath of fresh air ever.
i started following weekly at chapter 339, when Robin told Sanji and Chopper she was leaving the crew. I remember back then, I at one point speculated kaku would be the 8th crew member.
Like most people I started with the anime and then read the manga, but I read the manga after each arc in the anime. Once I started to catch up, I stopped with the manga and went anime only so I could read the Water 7/CP9 arc after. My first weekly chpater was this though.
http://view.thespectrum.net/series/one-piece-volume-01.html?ch=Volume+46&page=19
I started to following weekly after found a scanlation of chapter at the moment of Brook joined on my buddy computer. And began search it.
I actually read One Piece chapters before, then stopped. I blame 4kids version for it, but my true first weekly chapter is 454: Hummer. I saw a RAW page scan of Nami against Lola, and the funny line Nami: "I'm a Man!", really had me surprised. Then found out she was just saying that to avoid getting hurt hahaha. So after that I jumped back into the anime and manga, and haven't stopped, yay! 
Read some OP in American Jump like 8 years ago, but really…
491: Flying Fish Riders
"my name is Franky"
good times
My first chapter was 442, just in the beginning of Thriller Bark Arc, February 2007.
I caught up when Kuma had just shown up at Thriller Bark, http://www.onemanga.com/One_Piece/473/01/
I even read the spoiler for that chapter, right after I finished 472, because I was in such a hurry to continue reading. I've been hooked on spoilers ever since…
During the Skypiea Arc, beginning of volume 29…so around chap. 265-270
must have been in in the middle of w7… i can remember that the subbing groups then were really slow and I didn't want to wait a whole week to continue the story, so I switched.
Chapter 384 - Give The Signal To Counterattack.
I've been waiting for each chapter patiently from week to week since Alabasta started. So about volume 18 155ish.
I think I started following weekly with scans somewhere in the middle of Impel Down.
Mine was the chapter after they finally take down Oars, though I forget the title and number.
My friend showed me the First ep of the anime and I wasnt quite hooked until the preview of ep 2. He told me to watch ep 2 because my favorite character was going to be introduced :3 This was right around the time of the baratie arch for the anime. I went internetless for a while and when I picked it back up I was left on the vivi getting shot cliffhanger. So i picked up the manga here at ch. 132
http://view.thespectrum.net/series/one-piece-volume-01.html?ch=Volume+15&page=99
ace and blackbeard's fight
Arabasta arc. When Ace shows up. lol
towards the end of CP9 arc, I don't quite remember the chapter however.
Mine was during Arabasta arc Chapter 160.. I think is when the Baroque Works agent number 0-4 is gathering… http://www.onemanga.com/One_Piece/160/
holy shit. I was feeling smug with water7, now these alabasta guys show up
I started reading it on US Shonen Jump.. So it was the very first chapter, but following scans.. :S
Its kinda weird I first spoiled myself around 4 years ago back when the crew was in Enies Lobby (I recall it was one of the chapters in which Kaku was in his giraffe form) and following scans weekly.. Probably around chapter 570s
