SubscribePeople have trouble when they first hear about Twitter. They can't get a handle on what it is. It's whatever you want it to be. Your usage patter will probably match mine. Heck, my usage pattern this week probably won't match mine next week. Not only is Twitter evolving, but it evolves at different times for different users. I think Rands has a really good handle on the important points of Twitter here.
Every couple of weeks, a meme stressing about 'an increase in Twitter spam' wanders the Internet. Each time I see this meme appear, I turn away from my keyboard and bang my head against my desk three times.