Mostly at the instigation of dude_the, I have gotten myself a Twitter account. I was pretty uncertain about it until I found that Twitter and Facebook have an application which facilitates cross-platform updates so I can update my status in Facebook and have it automatically go to Twitter (or vice versa—not sure which platform the app. originates from). Shiny geekiness.
So if you Twitter, add me and I'll add you so we can follow each others' 140-character or less status updates .
Twitter essentially has the same function/purpose as status updates on Facebook: short, one- or two-line posts that friends can follow to see what you're doing right now, as compared to a longer, more detailed blog post. Twitter updates can also be sent/received via SMS on your mobile phone, a feature I haven't and don't plan to use, since I don't have a text message plan on my cell phone and each text therefore costs $$.