Twitter has added more than 100 million users this year. That’s a pretty extraordinary rate of growth for a company that just a year ago was thought to have peaked.

The growth can be partly attributed to Twitter’s smart focus on mobile. The acquisition of Tweetie, for example, the iPhone app that has since been rebranded as simply Twitter, brought a great version of the Twitter experience to smartphones. Since then Twitter has rolled out apps for Android and BlackBerry users too and mobile use has exploded.

Another significant factor in Twitter’s success this year is its emphasis on Twitter as a passive experience. Evan Williams, Twitter’s co-founder, has spent most of the year explaining that “you don’t have to tweet to be a great Twitter user”.

It’s a message that’s beginning to get through. Whether you want to follow the activities of celebrities or politicians, if you . . . → Read More: Twitter’s great 2010 shows it’s about more than what you had for breakfast