I was just reviewing the Google Analytics stats for the month of January for AgileWebDevelopment.com, the home of the Rails plugin directory, and saw some interesting numbers.
The number of "absolute unique visitors" for the month was 12,295. Those visitors logged 22,814 visits and 75,890 page views.
I would guess that AWD isn't necessarily one of the first sites you would see when you are just casually gathering info about Rails, but instead probably gets most of its visits from people who are actually using Rails. If that guess is true, then I'll also guess there's about 10,000 Rails developers out there (discounting the 12,295 number a bit for cases like one person at multiple computers, casual browsers who found the site but aren't using Rails, etc.). That's cool.