While I have not signed up, I feel I can nonetheless claim that it is pretty much completely useless.
Twitter is similar to Instant Messaging functionality, except public. You can post quick notes about what you are doing and where you are at this exact moment.
The world is dying to know these micro-details of your life after all!
In reality, I don't think even your friends want to know. Even I don't care about such mundane details of my own life!
Steve Bryant in his Today in Stupid blog sums up Twitter's inanity and annoyance "Of all the masturbatory ego-fluffers on the Web, nothing chafes me worse than Twitter".
I have seen one good use of it though. The colleague who introduced me to Twitter has a blog, Bargainista, devoted to Toronto shopping. Twitter has a widget that she has posted on her blog that allows her to post her up-to-the minute specials, sales and shopping discoveries. It does facilitate quick and easy micropublishing that works for this subject.
But upon looking at overall Twitter community's postings, I see: "refgrunt: can i borrow your cordless phone?", "tina is ready for the weekend", and "Eatin some rice cakes bigger than my freakin head".
Twitters of contemptuous laughter...
Addendum (posted March 29)
Another person shares my annoyance at Twitter. David Ewalt writes in Digital Download
A Note To All Twitter Users:
I'm not interested in what you had for breakfast. I don't need to know when you leave for work. Got stuck in bad traffic? Keep it to yourself.Let's hope Twitter is one of those embarrassing web fads that quickly dies, like Schnappi Das Kleine Krokodil (okay that had way more lasting power and interest than Twitter does)
Your work habits aren't even important to your coworkers. Your lunch choices matter to no one. Now you're reading your favorite blogs? Color me uninterested.
When you leave work, I don't want to hear it. If you go out for drinks, keep it between you and the bartender. And when you get home, don't share your TV viewing habits. They're about as interesting as watching paint dry.