2009 was an immensely important year for Twitter. The notoriously feature-shy service was largely turned into what it is today by its users. Originally, features such as retweets and hashtags were forged by the user base, not the developers. Furthermore, third-party clients such as TweetDeck and Seesmic raced to add the features that Twitter itself was lacking.
In late 2009, the folks behind Twitter decided to take a more active role in the shaping of the service by adding several important features, most notably Lists and built-in Retweets.
Adding Lists was a no-brainer. Twitter users pined for a tool to organize their friends into groups since Twitter’s beginnings. Retweets, however, were a slightly different take on the feature first invented by the community. Making such a change – even if it’s a subtle one – took some guts, as the community often greets such interventions with hostility. Luckily for Twitter, there were no mass riots over matters of retweeting.
The Growth Suddenly Stops
During the summer of 2009, problems began to pile up again. Twitter (along with several other services) were more or less permanently blocked in China. More importantly, they stopped growing in the US. After their amazingly fast growth during 2008 and the first half of 2009, we assumed it was an anomaly. But it wasn’t. According to Compete, Twitter’s traffic has flatlined, and co-founder Evan Williams eventually admitted that their US traffic had stalled. And in the world of web startups, once you stop growing, the cheers and confetti soon get replaced by mockery and, ultimately, oblivion
Twitter’s future is still uncertain. We still don’t know the overall business plan beyond a few hints at at least some current revenue, and we still don’t know if the service’s huge popularity boom in 2009 was just a passing fad. One thing is certain, though: The Google deal was the adrenaline injection Twitter needed. If Twitter is really destined to become the world’s new SMS, 2010 is the time to do it, and we’re happy to be along for the ride.
ref; - mashable