Do you mean on this site? In America, around the world? What are your parameters?

This article is dated, not sure of the original time since the link points to a page no longer available, the only date in the article is 1995, but states even then that genealogy is a $200 million dollar a yr business.

"Today, there are at least 100,000 such sites, according to Cyndi's List, a service that catalogs genealogy links. On Ancestry.com, which offers everything from Census data to message boards where long-lost relatives can connect, membership has doubled to 400,000 in the past year."

On a new genealogy social networking site: genealogywise.com, there are currently 18,037 members from around the world. There are 3,496 groups of all descriptions.