The feature is a new version of facebook groups, the difference from the old lame groups being that other people can tag you in groups, and you can control which of your information is shared with which groups. In other words, you could end up in groups with your high school friends, your college hall-mates, and your nerdy "set" club-mates and share information privately within each group, all without doing any work to assemble or join any of the groups because other people have already tagged you in them (ya know, the same people who already uploaded and tagged hundreds of photos of you since you don't even own a camera).
Though the new groups feature may seem ideal for restricting who sees that photo of you rolfing off the balcony, I predict it won't change people's facebook behavior much at all. There's this weird thing about facebook communication: more openness seems to make it easier, and less awkward, for people to communicate with each other. Like, when facebook first started, I don't think anybody divined the destiny of the facebook wall post. Originally, your "wall" was just a place for friends to post text. It seemed logical to post something about someone, to tell a story to add to that person's profile. (Incidentally I am appalled to find out that facebook wall posts before 2006 year have all been deleted, so my quick ten-minute research project into the original flavor of wall posts will have to go unfulfilled for now.)
Soon enough facebook walls became--or maybe always were--a place for direct (and boring!) communication (along with thousands of bland birthday wishes from people you will never communicate with ever again). What's the deal with that? There's no logical reason people should communicate via facebook wall posts. Anyone who can post on someone else's facebook wall could just as easily send an email or a facebook message, sparing the rest of the world the burden of reading our lame personal questions. I mean what's the point of adding "hey how's Chicago?" or "happy bday" to someone's profile, if all you want to do is actually find out how Chicago is or wish someone a happy birthday?? Clearly, the defining aspect of the facebook wall post is not communication itself, but some sort of meta-communication. You're not just asking a question to get an answer, you're also, in effect, saying something else.... possibly: "well I was already on facebook, and since I was already looking at your profile since you came up in my news feed, I thought I'd say hello, meanwhile saving myself the extra 3 seconds it would have taken to send a message instead. In fact, our relationship probably couldn't handle a personal message; that'd just be weird! I'd rather let everyone else know that we're communicating, to make this a more casual interaction." Or something like that. Isn't that weird?! Well, now it's pretty normal.
The point being, I think people dig this general openness of their communication and status updates. Sure, some things we want to keep more private. But most of those things we put in e-mails, text messages, and calls anyway. Facebook is the place where we project ourselves to all our friends, even, and especially the ones that we don't communicate with through more traditional means. Take this status update I just saw: "To the clubbers who park on my street on the weekends: shut the f*** up." It's a quintessential, complain-to-everyone-type update, with no real chance of ever reaching its intended faux-audience. In the new era of facebook groups, who among her friends would this person exclude from seeing this status update? No one! Perhaps because she hopes that one of her thousands of "friends" is one of those assholes who goes clubbing on her street on the weekends. It's a put-it-out-there-for-all-to-see-type thing. As is most facebooking.
Maybe I'm wrong and the new groups will totally change the way we use facebook. But I won't be surprised if people just get annoyed with groups and pretty much ignore them. I know I will!