Over the past few months, I have found myself in conversations about Twitter. Judging from the way people have voiced their preconceptions, Twitter is one of the more misunderstood websites on the intertubes, with common misconceptions including "Why would I want to read about every little thing someone is doing?", "It's just the latest fad" and "I don't know anybody on Twitter". Trying to avoid sounding like a shill, I would like to address these misconceptions.
Twitter is usually described as a microblogging service, a term which is not really descriptive but slightly disingenuous. Users write 140-character tweets. They can select other users to follow, thus building a stream of tweets that, hopefully, matches your interests. They can reply to or mention other users. It's also possible to retweet or "RT" a tweet, distributing it to your own followers.
This misses the point. Twitter provides three main things: identity, a voice, and the ability to build channels from other users' voices.
Supporting this, it also provides numerous ways to find different voices to add into the mix, with searches, and links from other tweets, and trending topics. Unlike other social networks you are generally free to follow whomever seems interesting: your voice is public, your followers are not your friends but those interested in your tweets.
Your identity, tweets and channels can be used on third-party sites as well as Twitter, which means that Twitter can be used as a platform for other applications. Whereas Facebook provides a photo albums tool - like it or lump it - use whatever photo-sharing website you like with Twitter. There are several in widespread use. It's quite a democratic system. You can often log into third party websites with your Twitter identity, tying your actions there to your Twitter voice.
Twitter is more like IRC than blogs; the short tweet length demands snippets, ideas, jokes, links and - though it's not quite a 'real-time' as IRC - it's quite possible to conduct a conversation.
People do not tweet about every little thing they are doing. Such a Twitterer would not be interesting to follow. It's not just the latest fad; it's a platform for sharing news and interesting tidbits that has already broken major news stories, made and buried film releases, and on which is built a rich and growing collection of social tools that, unlike Facebook, compete with and improve upon one another. And you don't need to know people, because there are already thousands of people tweeting about exactly those things you are interested in. Follow them, reply to them... maybe you'll even make some new friends. When's the last time you did that purely on Facebook?
The best advice I can give to anyone who has heard the buzz about, but didn't "get" Twitter, is just to try it. Twitter is new, and people are constantly discovering new ways to use it. Tweet about what interests you. Follow people who interest you. If you do, you'll probably find Twitter interesting and engaging.