It's very similar functionality to @replies on Twitter, and most folks will be pretty familiar with how it works and why you'd want to use it. Still, there are some differences to note, and some may appreciate a basic walkthough of how the new feature works.
Facebook's version of the feature, like Twitter, also uses the @ symbol to invoke. However instead of having to simply know or remember the person's username you'd like to tag, Facebook will generate an auto-suggest dropdown based on what you've typed after the @ symbol:
This is a nice touch considering that the scope of Facebook's status tagging feature goes beyond just being able to tag your friends. You can also tag pretty much anything you're connected to in the Facebook universe: companies, brands, artists and shows -- anything that has a Facebook Page. You can also tag events and groups you're a part of.
Once the item you're wanting to tag appears in the list, all you have to do is click on it to select it and include a linked version of that entity in your status update:
Unlike Twitter, the @ symbol won't actually remain as a part of your update; it's merely the syntax that invokes the tagging feature itself. Instead, the full name of the person, page, event or group you tagged is now contained in your status update, contextually linked to its actual page. When your friends see your status update, they'll be able to click on any of those links to find out more and possibly friend, fan, join or attend whatever you linked to:
Here's an example of using a status update to tag an event:
And here's the result after I've selected the correct event I want to tag in the update:
One complaint we have about the new feature is that it only works in your status updates, or if you post to someone else's wall using the Share widget on their page. That means you can't tag anyone inside of comments, which to us -- and probably most other folks who are used to Twitter's implementation of this feature -- seems like a "missing" feature. It doesn't really matter where the conversation is happening, and I may have occasion to want to tag something inside a discussion thread just as frequently as I might in a status update.
Apparently we're not the only ones who have griped about this already, because Facebook's Randi Zuckerberg mentioned in a spot on CNN today that a lot of folks had been requesting tagging within comments. She said Facebook is now considering that, and "it may happen." We'll be keeping a close eye on it of course, and will let you know if and when we hear about tagging coming to comments as well.