Let's break this down into 2 parts. What is Twitter and instead of asking why people flock to Twitter, let's ask the question of how people are using it. I'll tackle this as a list, because people like lists.
These updates, or tweets as they are called on Twitter, allow the user to share messages, status updates, what they are doing to anyone who has decided to follow each tweet and really connect with their followers. Members can get these updates via the twitter website, an RSS feed, text message, email, a number of applications including other blogging, social media web sites and so on.
Twitter: What's the Big Attraction? (or as my Sig-O says, "Why on earth would total strangers care what you're up to?")
Networking: Since it's so easy to find people who share your interests, Twitter is an outstanding way to make social contacts. Someone whose business is highly specialized can find this benefit especially attractive.
Marketing: You need to market yourself, just like big companies such as Dell and Comcast market themselves. Whether for a big company or just for you, a strong brand is very important. You need to let the world see who you are and what you have to offer. Try marketing yourself via a social networking site like Twitter. It worked for me.
Getting Ahead on the Info Wave: On Twitter, I hear the latest info on almost any topic you care to name -- before you hear it on the news. For example, the last time a big earthquake hit the Bay Area, the news was all over Twitter at least 10 minutes before CNN caught onto the fact.
It is so fun! You get to meet so many different people from all over the world. You can find a person to chat with about whatever you want!
Twitter is an uncomplicated and user-friendly site that you must check out if haven't already done so. It allows you a number of ways to "cross post", a term that refers to posting a unique status message which gets displayed on various social networking sites (irrespective of their names).