Based on popular domaining, auction and backorder websites, Daily Visitors, bids, views and general interest of the public etc figures, I estimate the number of domainers is about 50,000-150,000 or more.
Many people from different countries may enter Domaining in some point in their life.
I estimate the current the number of developers who look for domains is in the thousands.
I estimate the current the number of companies who look for domains is in the hundreds.
*With the increasing demand of premium domains and the growing number of unavailable "premium" or decent .com or .net or ccTLD domains, it is more than likely that the number of companies / developers who scour expired & drop lists every day will increase.