I lurk at DU often. They claim 52,463 user registrations since January 2001.
I don't doubt this number. I suspect however, greater than 30,000 have been tombstoned, if not over 40,000.
I know at least 50 names tombstoned are mine!
I have also repeatedly seen threads on DU asking how many registered users there are and the reply from the mods and Skinner (the owner) has been that that information is private.
I wonder how many non-tombstoned users they have that have posted at least once in the past month. I would like to see that number for FreeRepublic as well.
Ideology aside, I'm consistently impressed with how superior FR is to DU. The format is just better. We allow everyone to do searches. Every single relevant story gets posted within minutes if not seconds. The DUers clog their threads with ridiculous animations. They never post full articles only excerpts. Hours or days pass without major stories being posted, especially if it's negative to their side.