Hi Sean! Moved the discussion to the Other group.
4,800+ are the registered members, stats. We also have about 20,000 unique DC visitors monthly.
From them we have about 3,000 visitors who come directly to the site - so we can assume as "real" developers who reads/writes on DC daily. But this touches only the English world. And not all of them know about DC.
My evaluation is 10,000-15,000 developers worldwide.
E.g. last the IT Planet contest in Russia this year gathered 2,400 participants for InterSystems contest (mostly students). Should we count students as developers? Today maybe not, but tomorrow...