A couple of points regarding the article;

• the chart is US only. How come everytime Facebook traffic is measure its global then Twitter is US only.
• Would be more interesting to see global trends
• As many social media/tech watchers have pointed out. Twitter is protocol-like in the sense that a LOT of apps and website access it thru their API, those traffic are not accounted for
• The chart is a more accurate metric for measuring new users in the US which is stagnating.

A more salient point is how the new Retweet, List and stability has failed to impact growth in the US. I am willing to bet that API firehose open to all, localizations and more creative apps like our http://twidl.it will be better drivers of long-term user growth.