"When we launched the new 'Posts by me' setting, we showed a tool tip," he said. "The first time a user posts with 'Everyone' selected, they will see an 'about to post to Everyone' image. The first time a user changes this setting from the publisher, they'll see a 'changing setting' image."
And some Facebook users say they know quite well that once they hit the "share" button, their messages can be spread far and wide.
"Everything is public. If I put a picture up there or something like that or I post, I expect the public to see it," said James Wyke, a 29-year-old process engineer from Carrollton, Ohio. "If you put it on the Internet, it's not private."
He said he's been a Facebook member for about four years and has never been concerned about security or privacy.
On Monday, he posted, "cheated test. haha I just wanna be on openbook."
But he said that, jokes aside, he's very careful about what he says online.
"To me, it would be stupid to post something about my boss," he said.
But some industry observers say they wouldn't be surprised if there are Facebook users unintentionally sharing personal details with the world.
"I definitely think there are people sharing on Facebook, despite the warnings, who still don't get it," said Danny Sullivan, editor-in-chief of the tech blog Search Engine Land.
When Facebook forced users to update their privacy settings in December, he said the suggested privacy setting for status updates was "everyone," which may have shifted some to the most public setting without realizing it.
Even so, he said that for new accounts Facebook does "provide a great deal of support." While the default setting is "everyone," before users can share their first post they are told in a pop-up message box that their status updates will be "available to everyone on the Internet."
They are also told that they can change the default setting by visiting the privacy settings page.
"If you post something from Facebook, you should take responsibility for what you're doing," he said.
Still, Sullivan pointed out that though people post similarly personal ? and sometimes intimate ? messages on Twitter, the two sites come with very different sets of expectations.
Twitter has always been public and Facebook has historically been more private and friends-oriented, he said.
"With Twitter, it's all or nothing. With Facebook, you've got all of these settings, it may not be so clear that you're sharing to the world," he said.
Sullivan also said that while people may be accustomed to searching Twitter comments to see what people are saying, until Openbook came along, people didn't realize that Facebook could provide a similar experience.
Facebook users can search "Posts by Everyone," from the site itself, but it requires several clicks through Facebook search pages, he pointed out.
"[Openbook] is the first time where it has been very easy to see what people are sharing on Facebook, it just may not have penetrated people's awareness," he said.