Nielsen posted an update to their controversial report and in the process raised more questions than they answered. The biggest problem is Nielsen's original claim that user retention is critical to long term growth. While retention does play a role in growth, it is not as important as Nielsen states. As can be seen in the chart below, a website with over 60% passer-by traffic can still reach 20 to 50 million US UMV's. If you would like to see the data set, please check it out here. All of the data points were taken from Quantcast.
Nielsen posted an article on Tuesday titled "Twitter Quitters Post Roadblock to Long-Term Growth" claiming that Twitter had a 40% user retention rate. As seen above, I enjoy catchy headlines that rhyme, but Nielsen fails to mention one very important factor when evaluating Twitter traffic: It's only able to measure return visits to Twitter.com, but a large percentage of people using Twitter are using applications to tweet.