From personal experience, hiring for Ruby development seemed to get a lot harder and of the few candidates that applied, many couldn't do FizzBuzz.
I used a different screen (having people make change based on an arbitrary amount, so if the input was 81, you'd return [25, 25, 25, 5, 1], as we were in the USA) and it was also helpful. I didn't track the number of people that it stymied though.
(I always feel weird talking about interview questions publicly, but honestly anyone who prepares that diligently deserves to go to the next stage. If anyone's reading this because they're preparing for an interview with me and I ask this question, just mention this comment and I'll be impressed.)