I am not surprised to learn that Nielsen reports that more than 60 percent of Twitter users end up abandoning the service after a single month.

From Nielsen Online:

Twitter has grown exponentially in the past few months with no small thanks to celebrity exposure. People are signing up in droves, and Twitter’s unique audience is up over 100 percent in March. But despite the hockey-stick growth chart, Twitter faces an uphill battle in making sure these flocks of new users are enticed to return to the nest.

Currently, more than 60 percent of U.S. Twitter users fail to return the following month, or in other words, Twitter’s audience retention rate, or the percentage of a given month’s users who come back the following month, is currently about 40 percent.

Twitter is still something of a fledgling, and surely some other sites that eventually lived up to Twitter-like hype suffered from poor retention in the early days. Compare it to the two heavily-touted behemoths of social networking when they were just starting out. Doing so below, we found that even when Facebook and MySpace were emerging networks like Twitter is now, their retention rates were twice as high. When they went through their explosive growth phases, that retention only went up, and both sit at nearly 70 percent today.