I chose those terms to win easily. ;) buddycloud already claims over 500K users and seems to have significant momentum, some developer discipline, and is using

I chose those terms to win easily. ;) buddycloud already claims over 500K users and seems to have significant momentum, some developer discipline, and is using well-known standards, even if XMPP isn't everyone's favorite standard. And as others mention, you might want to count identi.ca too. If you think my bet is too paltry perhaps we can raise the stakes. However, note I said greater than 1M monthly actives, which is a more serious measure of traction than just user accounts.