Over 850,000 social networks on Ning, growing at the rate of over 3,000 each day (February 2009) and about 100,000 in January 2009 alone - http://blog.ning.com/2009/02/850000-social-networks-on-ning.html
Launched in February of 2007. By June, there were 60,000 Ning nets and by August, 80,000. At year's end, there were 150,000, and today, more than 230,000. About 40% of Ning's social networks originate outside the United States, and members from 176 countries have signed up, with the service already available in several languages, including Chinese, Japanese, Spanish, and Dutch.
The company estimates that, at this rate, by New Year's Eve 2010 it will host some 4 million social networks, with tens of millions of members, serving up billions of page views daily. One of the most popular Ning networks belongs to hip-hop mogul 50 Cent and has 107,000 members and counting. - http://www.fastcompany.com/magazine/125/nings-infinite-ambition.html
The company’s execution over the past 4 years has so far netted it 370,000 hosted networks (as of July 22, 2008). Net rating firms estimate around 3.5-4 Million users per month, so they average 10 users per network. Of course the reality is that if one browses Ning’s list of “popular” networks, one gets the strong sense that the vast majority of these networks were set up by tire kickers and promptly abandoned. - http://www.crunchbase.com/company/ning