I wouldn't describe writing a build script for Gradle as "using" Groovy. Most Gradle build files out there seem to be fairly short, usually 20 to 100 lines long, and consist of nothing more than the standard DSL calls. The template was probably copied from some other project, and the blanks filled in. I've yet to see a Gradle build script that actually drops out of the DSL to use Groovy to do any programming. The build script "authors" would have no idea how to use any of the more advanced Gradle API calls or Groovy language features beyond collection literals and closures. Gradle even still ships with the ancient Groovy version 1.8.
In Germany there was a Groovy craziness in JUGs around 2010, mostly coupled to Grails projects. At JSF days in Austria Oracle guys were discussing adding first class support for writing JSF applications with Groovy.
Fast forward to 2014, in our consulting projects when Groovy skills are requested, they usually mean that developer needs to take care of Gradle scripts.
Outside some banks in London City and the typical Fortune 10 companies like Twitter, Facebook and friends, there is very little uptake if you expand the spectrum to the Fortune 500 boring corporate world.
Which is the world I live in. Customers always ask for plain Java[1], since it gives them the highest value[2] for developer rotation.