Well we have over 992,000 users according @penguinpablo's most recent post..

So if we follow Facebook's path we should multiply 1000x by 2025!

1 million — End of 2004.
5.5 million — End of 2005.
12 million — End of 2006.
20 million — April 2007.
50 million — October 2007.
100 million — August 2008.
250 million — July 2009.
500 million — July 2010.
750 million — July 2011.
1.01 billion — September 2012.

Source