Looks like there are more and more Android Library created with Gradle build system. As I routinely go to Android Arsenal, almost all of library listed on it is created with Gradle. Gradle is supported natively in Android Studio, where in Eclipse we must add Gradle as a plugin. So, using Eclipse IDE is no-no solution.
Unfortunately, as I'm currently develop Android application with Eclipse, I can't go to import all my current application to Android Studio to avoid any problems on developing. Maybe after I finish my current application, I will trying to use the Android Studio and its Gradle. But for now, I'll stick with Eclipse.
For every beginner Android developer I suggest you to use Android Studio instead of Eclipse, because the future for Android development IDE is in Android Studio.