Today, finally, Zuckerberg did what critics — including MoveOn.org, which took an early stand in the case — had been demanding: He allowed people to turn Beacon off. He also made clear that when members do turn off the system, Facebook will not store information about your surfing habits that it receives from its ad partners.

As originally conceived, Beacon was a particularly egregious scheme for invading your privacy. Dozens of sites had contracted with Facebook to send people’s surfing data to the social network; your profile would send out little messages to your friends about what you were doing on those sites — telling them that you were shopping on Overstock.com, say, or were cooking certain recipes at Epicurious — as a kind of ad for those sites.

Not only did Facebook not allow people to turn off the system, it also assumed that if you did not explicitly prohibit it from sending messages out from each site in its ad network, you were granting permission. In other words, Beacon was devised as an opt-out plan — or, more precisely, it was plead-out, because getting the system to stop sending messages on your behalf involved a torturous number of steps.

Responding to the critics, last week Facebook fixed the system a bit, making the plan opt-in.

But it remained unclear whether Facebook was making use of your private data anyway — as programmers looked into the plan, they learned that even if you did not specifically opt in to Beacon, Facebook’s partners still sent the social network data on your behavior. That’s why it’s important that Zuckerberg has pledged not to store data about your actions on Facebook’s advertisers’ sites when you turn Beacon off.

In his post, Zuckerberg explains away Beacon’s problems as a failure to “find the right balance” between making Beacon easy and making Beacon safe.

Beacon, he says, began with the best of intentions: “We were excited about Beacon because we believe a lot of information people want to share isn’t on Facebook, and if we found the right balance, Beacon would give people an easy and controlled way to share more of that information with their friends.”

But in trying to make the system “lightweight” enough that it didn’t get in people’s way, the company overlooked its privacy implications, Zuckberberg says.

Worse, he adds, Facebook dithered in the face of controversy: “It took us too long after people started contacting us to change the product so that users had to explicitly approve what they wanted to share. Instead of acting quickly, we took too long to decide on the right solution.”

The explanation casts Zuckerberg and his team as well-meaning but bumbling, which is a tad convenient, because certainly a few other, more base considerations than mere incompetence prompted Beacon’s bad design.

For instance, money: As originally conceived, Beacon had one great thing going for it — advertisers loved it. Users didn’t have much choice in whether to send out alerts from corporations, and thus corporations were eager to pitch in to Facebook’s bottom line — which was certainly welcome news for Facebook, which has been groping for some kind of ad model to justify its investors’ huge expectations.

Will the new model hurt Facebook’s ad chances? Maybe in the short run. In the long run, though, it’s possible the company learned something from its misadventure — namely, to respect its members’ rights — that could yield larger gains.

To turn off Beacon, go to your privacy settings page in your Facebook profile.

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Here’s a video on the Facebook kerfuffle that I did for Current TV.

But Facebook did not completely address critics’ concerns. Specifically, it still is not allowing users to completely bow out of Beacon. Critically, this means that if you do something on a Facebook partner site, Facebook still gets information about your actions, whether you like it or not.

Beacon is a form of what marketers call “social ads.” It’s sort of the Web equivalent of word-of-mouth. When you do something on Fandango — buy a movie ticket, say — or one of Facebook’s other advertisers’ sites, the companies try to send out alerts, through Facebook, to your friends, in the hopes that they will follow your example.

Initially, Beacon gave people little choice over whether Facebook’s advertisers could send messages from you.

Now, says Facebook, the first time you use a Facebook partner site, you will be given a choice to opt in to Beacon alerts for that site.

Say you buy something from Overstock. When you next check your Facebook page, you’ll see a note asking if you’d like to send an alert about your Overstock experience to your friends. If you do nothing, Facebook does not send out the message.

That is progress. MoveOn.org, which had launched a campaign against Beacon, says that the move represents a “victory” for the program’s critics.

But because Facebook is not allowing you to completely shut down Beacon, there are still privacy problems with the program, as developer Nate Weiner points out on his blog.

Weiner says that when he visited to Kongregate, a game site that advertises on Facebook, he got a notice asking him if he’d like to send a Beacon alert to his friends. He clicked “no thanks.” But when Weiner analyzed what his browser did in response, he noticed that Kongregate sent data to Facebook anyway.

Weiner notes, “I’m not saying that Facebook is storing this data, there is no way for me to know. But they are without a doubt receiving it.”

Is there a way to prevent Facebook from learning what you do on its partner sites? Indeed, there is. Use Firefox, and install a plug-in to block Beacon.

Don’t understand what that means? The skinny: Members of Facebook can send out little messages to their associates that, per the network’s convention, must take the form, Member is {fill in the blank}. Things like:

But some people didn’t like that forced “is.” Folks regularly ignore it, writing status updates as if it weren’t there. This leads to messages like “Sarah is likes to dance,” a nice example put forth by Wired News’ Betsy Schiffman.

Schiffman also notes that hundreds of Facebook groups have formed to protest the verb. One of the most popular — Campaign to lose the mandatory “is” from status updates! — has attracted more than 64,000 members.

They argue that people would write more “creative” messages under an is-less regime. As examples of the sort of creativity they expect to flourish, the group offers these status updates:

Philistines! Have these people had never heard of haikus or sonnets or villanelles? Have they never heard of a dude named Gustave Flaubert, who once pointed out, “One must not always think that feeling is everything. Art is nothing without form”?

What Flaubert meant was that it is precisely an artform’s constraints — and not the lack of constraints — that juice people’s creativity; the Facebook “is,” no differently from Shakespeare’s iambic pentameter, forces people to look for interesting ways to say things.

Sure, if there were no “is,” you’d be free to write, “Nick wants a sandwich.” Boy, that really stretches the language, doesn’t it? Witness the creativity!

Instead of “Nick wants a sandwich,” why not, “Nick is starving for a sandwich,” which has the advantage of greater intensity. Or one of these others: