[wheels]

We track the programming language that our customers are using on sign up. Our customers aren't particularly early-adopter-ish, so I assume it's a reasonable approximation (taken over a decently large sample of sites):

http://blog.directededge.com/2010/05/30/what-programming-lan...

See also:

http://www.indeed.com/jobanalytics/jobtrends?q=ruby+rails%2C...

Or even (this one surprises me, since I figured Python generally would come out on top when not selecting for web stuff):

http://www.indeed.com/jobtrends?q=ruby%2C+python&l=