I love Twitter, but find posting from the Web a pain (via
www.twitter.com).. if I didn't use a Twitter client, I probably wouldn't have used it as much. Using Tweetdeck makes it just like using a messenger like Yahoo or MSN, except you're broadcasting to (in my case) over 600,000 people at once! It's alot of fun and I invariably leave Tweetdeck open in the background so I can tweet posts, urls, or what I'm doing when the mood strikes, plus I can interact with other "tweeters".
Great when you need help.. got a problem, just tweet it and someone will answer with a solution!
Twitter is also being used to twitter first hand accounts of the Gaza news, etc.
I have to admit.. when I first heard about Twitter, didn't interest me.. now I use it daily!