There was a Grails wave here in Germany, but now I seldom see anything related to it.
So I'm not sure how Groovy will fare in the future. Nothing seems to be taking its place, though, for testing and general manipulation of Java classes. Java and Scala are statically-compiled languages for building things, whereas dynamic Clojure seems to also be used for systems programming rather than scripting. I'm guessing Oracle will heavily promote Nashorn for scripting and JavaFX, but Javascript syntax doesn't seem quite as full-featured as Groovy for now.
Back in 2009 there was a big Grails wave here in Germany. Many JUGs had Groovy and Grails talks.
There was also some people trying to use Groovy with JSF. Myself I attended a session promoted by Sun hitting at possible official support after the JSF 2.0 release.
To the point we added support to it in our in-house JSF framework SDK, still JSF 1.x based.
Since late 2010 I have been doing .NET land mostly and now back on Java land, I hardly see any Groovy besides Gradle.
Same goes with other things: we had to write Groovy code to handle build cases which Maven plugins handle by default. That's mostly an ecosystem issue.
Are the sparse features, slow executes, and bugginess due to Gradle or due to the scripting language it uses? www.gradle.org/overview says they will happily support any community effort to create additional build script engines for Gradle. The Gradle developers had better do it themselves because after the Groovy++ fiasco, noone's going to put work into building something related to the Groovy ecosystem when it's likely to be skuttled and/or stolen later on.