I'd say there are about 40 or so users that are at least semi-active here on a regular basis, and 16 of us are active almost every day. As far as Users that have an account,I'd say probably at least a couple hundred, if not more (we're part of [Wikia so everyone who as an account on any one of their sites has an account here.
I wasn't sure about the wikia numbers, but from the Top Users list, I gather a little over 40 contribute a couple times a week, and about 10-20 more contribute about once every 2 weeks or so
