One of the most anticipated days in the history of social networking site Facebook has finally come: the company announced today that it has begun making status messages, photos and videos visible to the public at large by default instead of being visible only to a user’s approved friends.

UPDATE:After we wrote this post, Facebook HQ emailed to tell us that the first wave of users who get this feature will have their messages made public by default because their profiles were already marked as public, but that when they open the feature up to subsequent users – those users will have default privacy settings that match their pre-existing profile privacy settings. Unfortunately, in our tests so far (see our screencast) – we haven’t been able to successfully change our default message settings back to friends-only, it stays stuck on public. When we switch our test account from profile public to profile private and then back again, the default for message posting gets stuck at “friends of friends!”

So there are some kinks to work out here. However, it appears that we may have jumped the gun and assumed something that was not said in the Facebook blog post: that the experience of all users was going to be like the experience of the first users. The feature appears not to be working correctly and it certainly wasn’t communicated about well, but Facebook now tells us that it will not be opening things up quite like we characterized in this post. We apologize for writing a long blog post based on an understanding of the situation that appears to have been wrong. For what it’s worth – we think Facebook should get more messages out into the public so they can be analyzed, but we also think they should communicate carefully about privacy settings so that people can ease into it as best suits them. Read on for a discussion of the pros and cons of Facebook messages going public.

Private by default has been a hallmark characteristic of Facebook, as high on the list as the lack of MySpace garishness. It’s been key in making Facebook the biggest social network on earth. Now that’s about to change. Facebook has been very careful to avoid the major backlash that it has seen in the past when making substantial changes to things like privacy settings, but it’s hard to imagine there isn’t going to be a backlash. From a web innovation perspective, the move could lead to some of the most exciting developments we’ve seen yet from the world of social media.

Users can change their default privacy settings back to what it used to be – but that’s not in Facebook the Company’s best interests and we don’t expect to see site-wide prompts about this like we did about the availability of “vanity URLs.”

Update: Facebook just emailed us to say that they will in fact be making an effort to make sure everyone knows what their privacy setting is and that it is what they want it to be. From that email:

Your Publisher Privacy will stay at whatever you have set as the default. In addition, the first time you try to share something with the privacy control set to “Everyone,” you’ll be asked to confirm that this is what you want to do. If it’s not what you want to do, you’ll be able to change your setting before publishing.

The first time you change the setting on the Publisher control, you’ll be asked if you want to make the new setting your default, and you’ll be given a chance to do this in-line. You can also change your default at any time by going to the Privacy Settings Page and clicking on Profile. From there, scroll down to “Publisher Control Default” and choose what you would like as your default privacy setting.

Remember the News Feed?

When Facebook launched its News Feed feature in September 2006, displaying all activity by a user’s friends in a flowing list of updates on the page, the backlash shook the young service to its core. The News Feed is now the central feature of the Facebook user experience. The new public visibility of shared messages is going to change Facebook on that kind of scale.

Remember Beacon?

When Facebook launched its off-site advertising initiative called Beacon, users were seeing things like the purchase of a surprise engagement ring on exposed to a would-be wife on Facebook because people didn’t understand how to deal with the new integration of 3rd party sites. The backlash was so big that Facebook founder Mark Zuckerberg had to try and calm Barbara Walters down about it on national television. Beacon didn’t disappear but was reformed in a more palatable way. The backlash against public default visibility is going to resemble the Beacon backlash, if not dwarf it.

Facebook Naked

And now we’re at today. By default, all your messages on Facebook will soon be naked visible to the world. The company is starting by rolling out the feature to people who had already set their profiles as public, but it will come to everyone soon. You’ll be able each time you publish a message to change that message’s privacy setting and from that drop down there’s a link to change your default setting.

But most people will not change the setting. Facebook messages are about to be publicly visible. A whole lot of people are going to hate it. When ex-lovers, bosses, moms, stalkers, cops, creeps and others find out what people have been posting on Facebook – the reprimand that “well, you could have changed your default setting” is not going to sit well with people. We’re sure it won’t be retroactive and a lot of people will back out of being public, but it could still be a game changer.

Robots FTW

The soft fleshed creatures that we Facebook users are will likely hate the new setting, at least at first. But robots are going to love it. As the largest social network on the web, with an incredible amount of time spent on the site by its users, Facebook holds a giant reservoir of demographic and sentiment data. It is the motherlode – and it’s been inaccessible so far because everything has been private so far.

This winter there was a lot of discussion of a rumored “Facebook Sentiment Engine” believed to be in the works. We wrote about what could be both best case and worst case scenarios for the opening of Facebook user data to outside analysis.

Best Case

Think of the non-commercial, public interest kind of data that could be acquired. When the economic stimulus plan of 2009 was first announced on national television – what was the reaction of people in their mid twenties who lived in the Mid West of the US? Was that collective reaction substantially different from the reaction of self-identified queer people of color living in the North East US? How did the public reaction to the proposed plan change one hour, one day or one week after the announcement? This is all very interesting and potentially valuable data that could be, for the first time in history, available in near real time. Just by listening to what people are talking about in status updates and comments.

Worst Case

The worst case scenario is that Facebook will not open a free message search API for outside developers, instead it will make bulk access and analysis of all these public messages available only to commercial firms able to pay in order to harvest the data for marketing purposes. That seems pretty likely, unfortunately.

It’s notable that there is not yet an option to search publicly shared content, as in full text search of messages, on the Facebook search page. It may not be searchable at all, except through very specific and possibly paid access granted by Facebook – even though it’s all visible to the human eye. As Fred Vogelstein wrote in a long post on this week:

By Facebook’s estimates, every month users share 4 billion pieces of information–news stories, status updates, birthday wishes, and so on. They also upload 850 million photos and 8 million videos. But anyone wanting to access that stuff must go through Facebook; the social network treats it all as proprietary data, largely shielding it from Google’s crawlers. Except for the mostly cursory information that users choose to make public, what happens on Facebook’s servers stays on Facebook’s servers. That represents a massive and fast-growing blind spot for Google, whose long-stated goal is to “organize the world’s information.”

Comparisons to Twitter search are only useful in talking about theories of value, in terms of actual value an open Facebook search would leave tiny Twitter in the dust.

So there are two ways this could go. Free programatic analysis to the publicly shared information from Facebook users could be like a high-speed, real-time Library of Congress for all the robots in the Republic. Or it could be limited access, like the high-priced market research reports bought and sold by marketing firms about other pools of public sentiment today.

We know which scenario we’re cheering for.

We also feel pretty sure how most Facebook users are going to feel about this fundamental change. They are going to hate it like most residents of the Wild West must have hated the first US Census agents.

In time, though, people may very well decide they are comfortable with their social networking being public by default. That will be a different world, and today will have been one of the most important days in that new world’s unfolding.