Adam Lashinsky’s first recollection of Twitter hitting his consciousness was in 2007, when the service was about a year old:

I’m almost never an early adopter of these types of technologies. I see far too many of them, and almost all are as irrelevant when they start as when they die. I probably lumped Twitter into the same category at the time, if I thought about it at all.

What I recall is Chris Sacca, then a Google executive, telling me about posting to Twitter during Google’s Zeitgeist conference for is advertising customers in October 2007. (My other memory of that conference was a speech by the extremely fresh-faced David Cameron, then leader of the opposition in the U.K. and a seemingly long way from running the country.) I have a vague recollection of having no idea what Sacca was talking about and not quite grasping why this silly behavior—short-burst commentary to a tiny audience—was worthwhile.

Like others, I paid scant attention to Twitter as it grew in popularity over the next handful of months. Then, in May, 2008, I was sharing a car ride with Michael Arrington, then the editor of Tech Crunch, who explained to me that every time he wrote a post on his blog—and he wrote many—he posted a link to the post on Twitter. He also mentioned that he had some 20,000 “followers” on Twitter. BAM! That I understood. If nothing else, Twitter was a broadcast mechanism for someone like Arrington, and, potentially, me. It was a way to accelerate an already large audience as well as an effective notification tool to remind loyal readers to come back to one’s site. I signed up for a Twitter account shortly after. While I always did and always will write less frequently than Arrington did, I started posting links to my articles as well—and saw my audience grow slowly as a result.

Now that I grasped the significance and potential of Twitter, some time shortly after that I contacted Biz Stone and said I’d like to write about the company in Fortune. I was well aware that at that time the tech blogs, like Tech Crunch, had been covering Twitter obsessively and that Fortune would be considered late to the game. I didn’t care. Nobody in the “real” world had a clue what Twitter was then. It had about 3 million users.

That summer, I visited the company’s bare-bones offices in San Francisco’s South of Market neighborhood a couple times, meeting with Stone, Evan Williams and then-CEO Jack Dorsey, who wasn’t anywhere near the business celebrity and fashion icon he is today.  I wrote what I believed at the time was the first significant article in a mainstream publication about Twitter. (Please correct me if I’m wrong about that.) My article ticked all the predictable boxes about how meaningless this all might be and included an instructional paragraph for the uninitiated. (The latter holds up well: Difficulty in using Twitter, according to conventional wisdom, remains a barrier to growth for the company.) I also called Twitter the hottest kid in the burgeoning class of startups that was thriving in San Francisco, even as the financial crisis was afflicting the greater economy.

On my first visit to Twitter I remember the smallish staff gathering in the late afternoon for a birthday celebration of one of their own. As the team of exclusively young techies queued up for birthday cake or some other late-day snack, I stood on the outskirts of the scrum chatting with Ev Williams, a co-founder whose Twitter future still included helping ax Dorsey as CEO and then getting booted from the job himself. The room was loud from the boisterous employees and traffic noise from the street below, so Williams, a soft speaker to begin with, leaned over to me and said, “This thing is going to be really big. I mean, really big. Way bigger than blogging.”

Williams wasn’t wrong about that.

By late 2009 there wasn’t any doubt anymore that Twitter was for real. In fact, it was so “successful” that the clamor for it to prove its worth—by making money—was rising to a loud roar.

Twitter had now hit “tweenhood,” as Adam Lashinsky put it:  The service had 55 million users and no business model. “But that’s a touchy subject,” he wrote.

Turns out, however, the subjects would only get touchier…. 

Jessi Hempel had been using Twitter since 2007, but had yet to write about the company until she began digging in early 2011:

“I think I even had a ‘Fail Whale’ t-shirt as it had become a symbol of the both the popularity of the service and the tolerance of users,” she recalls. “Twitter was the only service I can remember that could suffer so much down time and still manage to become even more popular by the day. But by spring of 2011, something just felt wrong. There were two different narratives about the company. Outside of Silicon Valley, everything that had ever been written about the company was upbeat and fun and focused on how Twitter was just plain awesome. Inside Silicon Valley, Twitter’s undisciplined corporate culture and its relative leadership vacuum came up frequently. Why wasn’t anyone writing about this? It felt so simple I thought I was missing something—until I started doing the reporting….”

“Trouble at Twitter,” published in April 2011, related a remarkable tale of boardroom power plays, disgruntled founders, and more management turmoil at the high-flying tech company.

Less than two months later, Twitter co-founder Biz Stone left his management role—joining fellow co-founder Evan Williams (who vacated the CEO position the previous fall) and Jason Goldman (a former veep of product at Twitter, who departed in December) to relaunch the Obvious Corporation—the business that had initially hatched Twitter.

By November, we were asking: “Who is left?”

Not long after Jessi’s April 2011 feature ran, Adam put the question of Twitter’s management fumblings—and questions about the company’s advertising model, its frenzied growth, the threat of Google, an FTC investigation, and more—directly to the company’s CEO, Dick Costolo, at FORTUNE’s Brainstorm conference.

Now that the company has secretly filed for an IPO, the questions keep coming—indeed, there seem to be more of them than ever:

•  What’s Twitter actually worth today?
•  What’s the $1 billion question about Twitter’s revenue?
•  What can Twitter learn from Facebook’s hapless IPO?
•  And who’s going to get rich when the company goes public?

Five years from now, we imagine, we’ll still have as many questions as answers.