The new Groups will be set to "closed" by default, Facebook CEO Mark Zuckerberg explained during Wednesday’s briefing (which I caught via video feed). Creating a new group is a simple matter of adding a few friends, who in turn can add their own friends to your virtual Facebook community. Don’t worry: Anyone new who gets added to the group — including the name of whoever added the person — will be announced via an info panel, and you can always bail on a given group if you choose.

What can you do in a Facebook Group once you’ve created it? Well, there’s the obvious stuff, such as posting Group-specific updates or writing on the wall or sharing photos and video.

You can also do some more interesting things, such as creating and editing group documents (like, for example, shopping lists or the evening dinner menu), or you can engage in real-time group chat, a first for Facebook (which, until now, has only allowed one-on-one chat). You can also send an e-mail to the entire group using a custom e-mail address.

And what kinds of groups could you create? Based on Wednesday’s briefing, it sounds like Zuckerberg & Co. are hoping that groups will run the gamut from, say, friends and colleagues to everyone you know who’s into football, or perhaps just a small circle of your closest friends and family (who might me more interested in what’s in your lunch bag than everyone else on your friends list).

The new Facebook Groups will begin rolling out today, Zuckerberg said, and will replace the current public Groups functionality that you could previously restrict only to a Facebook network. But existing Groups will continue to exist, as well the (little-used, apparently) Friends Lists that you can create from the left-hand navigation bar. And yes, developers will eventually get a crack at Groups, although I’d imagine that a Group could block a Facebook Platform application in the same way an individual user can.

So what we’re essentially talking about here is the same kind of virtual workspace that you might find on an office intranet — or the failed Google Wave, for that matter. Instead of collaborating on projects, though, Facebook users will be using Groups to collaborate ... well, socially.

Zuckerberg said that Groups was revamped in order to address the "biggest problem in social networking": namely, trying to organize all your various friends on Facebook into specific social groups. The current Friends Lists feature on Facebook was intended to help users create such groups, but only about 5 percent of Facebookers have actually created a friend list, Zuckerberg said.

Another option was to use an algorithm that would automatically herd your friends into groups, but such a technical solution could easily make critical mistakes (like adding the plumber that you’ve been dealing with lately — Zuckerberg’s example — to your list of closest confidants) or work entirely too well (like prioritizing a, well, secret pal you’ve been messaging on the sly).

Allowing Facebook users to create their own Groups — with new members able to add their own friends — seemed like the most appropriate solution, Zuckerberg said.

Will users take to the new feature? Hard to say. I’m happy to see that the new Groups will be set to "closed" by default, but I wonder if allowing any member of a group to invite anyone else they want might cause problems. Then again, being able to create a small, private group of Facebook pals does have some appeal, especially when you want to share a bit of trivia that could be a little too trivial for your zillion other Facebook friends.