I find the conclusions in the article absolutely wrong. With every new "social networking" site that's come out in the last four years, from LinkedIn and MySpace to Facebook and Twitter and the various and sundry others, I personally have joined, played, then dropped its use within weeks.
But then after a few months, with the occasional check-in and addition of detail to a profile, or not, I have always found that I will one day just find how I like the tool and just be a regular user.
The question is not whether Twitter users will sign up and then never use it again. The question is how many of those 60% who drop Twitter will come back every couple of months and then start using it within a year. That 10 percent growth only accounts for a small fraction of the overall growth, which should be higher.