If you haven't tried (or heard) of Twitter, it might be time to give it a shot.
I signed up a couple of months ago after a friend told me about it. At first glance, it has the same feel as changing your Facebook status. That is, more or less, what it's like except it goes a bit further.
Simply put, you sign up and let the world know what you're doing. Or send a link to an interesting story. Or send out a link to your latest blog posting. Or, find someone to follow and get updates from them. It's a mini-blog of sorts. It's almost like having an RSS feed into people's lives. Some companies also use Twitter to send links to their press releases and/or stories. Here's one for CBC News: http://twitter.com/cbcnews
You can post and read the updates on the Twitter.com web site, or use one of a few third-party applications, widgets, and such. My personal favourite is Twhirl and I usually leave it open on my desktop at work and at home.
The people you follow don't have to be your friend. They don't even need to approve of you following them. They can block you if they wish. The same as you can block anyone from following you. Generally, you'd want to follow someone who has similar interests.
As I write this, I am following 15 people and I have 22 followers. I know ONE person that I am following, and one of my followers knows me (the same person)
Here is a good blog posting with tips on getting started with Twitter.
Here's my Twitter feed: http://twitter.com/twister65