A few months ago, analysts
were confident that the number of Twitter users would reach a million people even before the beginning of April of this year. Judging by the rate of growth of the subscriber base, right up to mid-February it seemed that it would be so. Moreover, the number of users grew even faster than predicted, so the millionth user had to register a couple of weeks earlier. However, in early March, the situation changed: the growth rate slowed down significantly, as can be seen in the graph.

If further growth continues at the same reduced speed, Twitter will overcome the one million users no earlier than June 2008. The experts have no explanation for why the number of new registrations suddenly dropped from 3,500 to 750 per day.
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However, the graph shows only open registrations that are tracked by the
Twitdir directory. The share of closed accounts is about 15%, so if you consider them, then Twitter already has a million users.
via
Twitter Facts