Twitter is listless no longer. Following in the footsteps of Facebook, the increasingly popular platform has given its users the ability to sort other Twitter users into lists. “The idea is to allow people to curate lists of Twitter accounts,” Twitter’s list feature project lead, Nick Kallen (@nk), explained.

For example, you could create a list of the funniest Twitter accounts of all time, athletes, local businesses, friends, or any compilation that makes sense.

Lists are public by default (but can be made private) and the lists you’ve created are linked from your profile. Other Twitter users can then subscribe to your lists. This means lists have the potential to be an important new discovery mechanism for great tweets and accounts.

We started working on this feature because of the frequent requests we received from people who were looking for a better way to organize information on Twitter.

The company began rolling out the feature last month, gradually expanding access among its users. By Friday, Twitter lists had been fully integrated. By Sunday, 6.5 million—yes, million—lists had been created. Twitter now features: humor lists and techie lists and breaking news lists and staff lists and World Series lists and health care lists and ‘wits’ lists and media lists and media thinkers lists—and lists of lists and feeds of lists and rankings of lists and guides to creating lists and guides to using lists and guides to choosing lists and guides to list etiquette.

And among those watching the lists roll out, we’ve seen the typical new-technology-rollout combination of existentialism (What Do Twitter Lists Mean?), proclamation-making (“Twitter ‘Lists’ Change Everything”), and hand-wringing (“Twitter Lists: I’m Not Down”)—some of it valid, some of it less so. Twitter lists are exclusive. (Of course they’re exclusive; that’s the whole point.) Twitter lists are a popularity contest. (Only if you let them be.) The lists are a pain to create. (Not really.) And, either way, they’ll likely increase online serendipity and engender a curatorial economy and create a more efficient page rank system and suggest new ways to measure influence and empower political activism and maybe even replace RSS readers as users’ content aggregator of choice.

The ultimate validity of many of these claims—be they of the listophilic or -phobic variety—remains, at this early stage, to be seen. One thing, however, seems clear: Twitter lists are likely moving us closer to the full realization of last year’s quote-heard-round-the-Web: “If the news is that important, it will find me.”

What that means in turn, though, is a shift not just as concerns the cold, hard facts of Twitter: ‘influence’ metrics and aggregative utility and ‘economies’ of various stripes, etc. In means a shift as well in the platform’s foundational function: Twitter is—in addition to, and in many ways above, everything else—a community. And it is a community, importantly, that has been essentially created by users: Twitter owes its current form to the innovations added, over the few years of its existence, by its users. Users created @ replies. They developed hashtags as a kind of real-time, proto-list, filtering feature. They devised Follow Fridays. They invented the retweet. They coined, in fact, the word ‘tweet’ itself—a shorthanded term for ‘Twitter post’ that Twitter, the company, initially resisted. (It failed.)

As Steven Berlin Johnson put it in his recent Time cover story on Twitter:

This is what I ultimately find most inspiring about the Twitter phenomenon. We are living through the worst economic crisis in generations, with apocalyptic headlines threatening the end of capitalism as we know it, and yet in the middle of this chaos, the engineers at Twitter headquarters are scrambling to keep the servers up, application developers are releasing their latest builds, and ordinary users are figuring out all the ingenious ways to put these tools to use. There’s a kind of resilience here that is worth savoring. The weather reports keep announcing that the sky is falling, but here we are — millions of us — sitting around trying to invent new ways to talk to one another.

What Johnson is describing, in clinical terms, is end-user innovation: decentralized development undertaken by a product’s consumers, rather than its suppliers. But what he’s describing more broadly is simply a collective—one with common languages, behaviors, ethical codes, rituals. A collective, in other words, that is also a culture.

And one of the more interesting questions in the whole What Do Twitter Lists Mean? discussion is what Twitter lists mean for the culture of Twitter—for the group-moderated behaviors that have thus far defined the platform’s existence. Twitter lists have an effect not only on Twitter’s infrastructure—its form and its filters; they may also, in a classic medium/message kind of way, come to affect the platform’s content itself. They will likely not only establish and solidify hierarchies among users, but also engender a kind of Pareto distribution in which the high-follower users gain more and more followers…and the less-followed users remain less-followed. The rich get richer, etc.

What we could also see, however, is a long-tail dynamic playing out not merely among the users of Twitter—the popular few, the plebian many—but also within the content of individual Twitter feeds themselves. Lists are limiting not only in the physical sense, but also in the definitional: in categorizing Twitter users—‘Funny People,’ ‘Smart People,’ ‘People Interested in the Mating Habits of Short-Nosed Fruit Bats,’ etc.—they generally highlight only one aspect of a user’s personality and then define the user according to it. But that narrowness could, in turn, encourage people to conform their tweets to the lists they belong to: for ‘Funny People’ to limit their tweets to funny things, ‘Smart People’ to smart things, etc. Rather than a hodgepodgy amalgam of people’s thoughts about whatever they happen to come across in their jumbled, chaotic, and category-resistant daily lives, we may soon start to see stratification. Twitter lists may shift the platform’s emphasis from people’s full identities to fragmented ones.

We may soon see, in other words, a shift in dynamic from ‘personality’ to ‘persona’—from fuller, unfiltered expression of whatever might pop into a user’s mind…to observations and links that hew to a user’s list-imposed identity. I’m on some ‘Future of News Thinkers’ lists, for example; I’m assuming that, generally, the people who follow those lists have no interest in my thoughts on the latest Top Chef, or on Orhan Pamuk’s latest novel, or on Glenn Beck’s latest foray into hyperemotive hyberbole. Aware of the disconnect between myself and @megangarber—aware of the categories that other users have placed me in—I’ll likely censor, much more than I did before Twitter lists entered our world, the bulk of the thoughts that cross my mind on a given day.

Now, granted, the vast majority of those thoughts fall somewhere on the continuum between ‘interesting only to me’ and ‘interesting not even to me.’ My self-censorship is a great loss to precisely nobody. And besides, you could say, what we need—in a media world whose noise-to-signal ratio is alarmingly high—is more self-censorship, not less. Everyone—me, you, the Twittersphere, the world—would be better off were we spared the kind of spur-of-the-moment, self-centered, unfiltered drivel that so infamously populates our media environment.

Here’s the thing, though: I like the spur-of-the-moment, self-centered, unfiltered drivel. I like learning the little quirks of people whose ideas I admire, whose work I follow. I like learning what movies they watched over the weekend, about the cookies they baked with their kids, about the novel they’re reading just because. I even, yes, like knowing what they had for breakfast. There’s immense value in those minutiae: for all the talk of the Web’s tendency to separate people into their own carefully curated worlds…Twitter does just the opposite: it allows for engagement without pretense. It assumes—indeed, it pretty much requires—spontaneity. It counters atomization with humanization.

Dave Winer famously called the Web log, back when the platform was still a novelty, “the unedited voice of a person.” Today, that role has fallen to Twitter. Increasingly, blogs are for fully-formed thoughts and ideas; increasingly, Twitter is the platform for spur-of-the-moment musings, for quick-take reactions, for tumultuous randomness. For the unedited voice. Lists—which curb serendipity even as, in other ways, they certainly encourage it—will filter the noise for us. This is the good news. But it’s also the bad news. There’s a fine line, after all, between self-awareness and self-consciousness; and the more we filter our voices—the more we categorize them, and organize them, and treat them as commodities rather than expressions of identity—the less fully human we allow them to be.

Megan Garber is an assistant editor at the Nieman Journalism Lab at Harvard University. She was formerly a CJR staff writer.