Fine, what I really meant to say was "accounts", not "users". In my framework, I only consider "users" those who signed up, so I usually refer to accounts as "users", but technically this may be incorrect.
There are 20 million accounts, 125 thousand active accounts [1]. The number of people who refer to Wikipedia is probably over a billion, since it's often the first hit in Google (speculation). Roughly 25% of edits are anonymous (no account), and anonymous edits are significantly longer than non-anonymous ones [2].
