I don't know of any other project using it. We are always doing Maven or Ant.
If Gradle is the future I hope it gets improved, I gave up on Android Studio given its dependency on Gradle and how it drags my dual core with 8 GB to its knees when compiling.
That could be the slow, dynamically-typed Groovy in Gradle that's dragging your machine. Gradle needs to bundle another build language. Since the goal of statically-typed (and hence speedier) Kotlin is to make it easier to write IntelliJ IDEA [1], on which Android Studio is built, instead of using Java, the logical choice is Kotlin.
Gradle's developer says they'll happily support any community effort to create additional build script engines other than Groovy, but it isn't a priority for them right now [2]. Perhaps the Kotlin team need to kick off a Kotlin build engine for Gradle (though because one of the Kotlin developers was a victim of the Groovy++ fiasco, I'd understand if the Kotlin people are hesitant about having anything more to do with Groovy ecosystem software like Gradle).
[1] http://blog.lunatech.com/2011/08/24/scala-ceylon-kotlin-goal...
So far I have been using the Eclipse ADT/CDT for my hobby development, mainly with C++ (just graphics stuff).
Then I thought to try out Kotlin instead, but could not. It was worse than waiting for my NDK C++ builds to finish, with the whole computer at 100% CPU usage.
I ended up filing a ticket, like many other developers already did.
I also know that Netflix use Gradle for pretty much all their Java stuff.