I signed up with Twitter very early on (this was when they had only a few thousand members), but didn't get it at all. Little did I know what lay ahead once political events started being Tweeted and covered by the press. How quickly that membership exploded!
Several years would go by before I finally figured out how I could integrate it with my site. Today I have about twice the amount of Twitter followers than Facebook.
The real genius of Twitter is the 140 character limitation that encourages a fast pace both for content generation and consumption. It's an echo of the age of the telegraph where messages were brief and to the point. Brevity equals velocity (in other words, speed is king).