ReadWriteWeb has a post today titled “Twitter’s Big Day”:

Twitter has gone mainstream. Late last night, Ashton Kutcher (@aplusk) became the first Twitter user with more than 1 million followers. Today, media mogul Oprah Winfrey sent out her first tweet and will dedicate a full episode of her talk show to Twitter.

That is a big day. Kutcher had been in a race with CNN to be the first Twitter user with a million followers. It’s not too long ago that there weren’t even a million active user on Twitter in total. At the beginning of 2009, there were barely even one million for each of the two contestants:

Our 2008 retrospective (still a developing story, as this post demonstrates) started by asking the question if 2008 was the year of micro-messaging—the year of Twitter. In part, we wondered if perhaps “the real question is whether 2009 will be the Year of Micro-messaging.” At the end of 2008, it sure seemed like Twitter was getting a lot of buzz. Little did we know we hadn’t seen anything yet. The extent to which the service went mainstream has been unbelievable. As we posted recently, there’s strong evidence that Twitter is becoming so mainstream that it’s not really the domain of early adopters anymore.

Between becoming culturally mainstream and doubling its unique visitor volume in a month, Twitter has already made 2009 more about itself than 2008 was. In December we noted that “[it]t’s important to keep perspective. Facebook is 30 times larger than Twitter and still growing at a phenomenal rate. It adds about as many users in a week as Twitter has in total.” But now, even keeping things in perspective, it’s hard to ignore the momentum Twitter has at this point.

And numbers aren’t the whole story. Take a look at this photo our designer Zak took in the subway recently:

Those stickers are promoting Diddy’s Twitter identity. Who knows if they were put up by paid agents or simply by fans. Either way, the television show advertisement has become a background for something more dynamic, participatory, and exciting.