The subject of twitter came up but her brain was full from other things and in lieu of dumping on her in a format that requires too much social attention, here's some stuff about the service, behind an LJ cut to save my twitter-allergic friends.
twitter.com hosts a database of very short messages, 140 characters maximum length. Each message contains the username they were posted from, the datestamp for when they were entered, and the text of the message, and possibly the name of the tool which posted them. There appears to be little else.
Messages can be posted from the webpage, or by message from a registered SMS-equipped cell/IM service sent to 40404, or from one of several other non-browser interfaces that use the twitter API.
You can tell twitter thatn you want to "follow" another username - actually, a LOT of other usernames.
You can designate a username to be public or private. Private, only displays messages to the people on the list you are following. Public, anyone can read them. Twitter displays your messages on a special webpage
(http://twitter.com/yourUserName) which can be viewed by anyone, even if they don't have a twitter account, if the account is set to public. If it's private, they can only be viewed by (yourself and) people who are on your follow list, when they are logged into the service.
There are some related services, one for shortening URL's (since they are frequently way too long to fit) and one for hosting pictures, and a number of semi-related services for finding people, etc.
Names and Special Commands:
@name is how you refer to the name of someone else.
For instance, @foomf is my account. Using @foomf in a string will make it show up to searches for posts containing that name.
#word will automatically create a tag, and you can search for that tag string and find related posts. This has been used to generate communities, both transient and long-lived; the web interface code will pull in those searches if you click on them in some other message.
I have seen it compared to a wall of graffiti, a loud party where you can only hear short sentences, as SMS messages that you can direct to groups, and as an infinite refrigerator on which you can post your own little yellow sticky-pad notes, only each person's notes are in a slightly different color, and you have special colored glasses that let through the colors of the notes from the persons you want to read.
How People Use It:
Some people use it in lieu of a journal, but their entries are brief. Very brief. Some people use it as a platform for widely distributing their messages - Obama used his twitter account quite a bit but has had to go on a four-year-minimum twitter retreat, since the rules on electronic communication around the White House are quite complicated and amazingly antiquated as well.
Private v. Public:
It's a bit less flexible than Livejournal, but you can have multiple accounts, each focussed on a specific thing. Private means you won't get spambot followers. Public means you almost certainly WILL get spambot followers, which you will have to either ignore or better yet, block.
Public is pretty helpful, if not absolutely necessary for any account where you plan to do community-based stuff.
Community equivalents: There was a quick community created for the Australian bushfires earlier this year. There is a "missing/exploited/amber-alert" community. There are many others.
Why I hate the name:
It's too damn cutesy. Yeah, I know "it's birds tweeting" ... It's a bunch of people blithering, blathering, and blurting is what it is. "Following" ... I prefer "stalking" but at least it's better than LJ's "friends" paradigm which doesn't actually mean that they're in any way friends.