Three research firms reported traffic to Twitter.com dropping between the month of September and October. According to these firms, the number of unique US visitors to the Twitter website went down from September to October, from -2.1% to a staggering -27.8% --the latest figure meaning that the number of unique US visitors dropped from 26.2 to 18.9 million unique visitors in October. These reports fueled several comments, spelling troubles for Twitter or stating Twitter's decline.
However the same report also mentioned that in August 2009, 43% of Twitter users accessed the service through 3rd-party applications, and 19% through SMS. Thus a large chunk of Twitter usage is not accounted for, and numbers based on twitter.com traffic only cannot be seriously interpreted.
Indeed, if we compare the August 2009 figure with today's data, Twitter's website users share went down sharply to less than 21%: TweetStats data shows that the twitter.com website, as of Dec 2nd, 2009, is responsible for only 19.19% of all the tweets, via 20.75% of the Twitter users. The most popular 3rd party Twitter client, TweetDeck, produces 17.01% of all the tweets via 13.23% of the Twitter users.
Today most of the people use Twitter clients other that the web site, and the trend is that 3rd party applications shares keep increasing. Also note that the number of tweets increased as well, to about 27.3 millions a day as of mid-November, even though it is difficult to make out the part of spam in that number. All signs point to an increase of Twitter usage, unlike many have concluded. Twitter is well on track to reach 18 million US adults by the end of 2009. Twitter is here to stay and grow.