The Ehcache project is happy to welcome Grails to the fold. The new Grails 1.2RC1 uses Ehcache as the default Hibernate second level cache. We worked with the Grails community to test Ehcache with Grails to ensure a good developer experience. As part of that we have added a new Grails Chapter to the Ehcache documentation on how to configure Ehcache for Grails, including production tuning.
We plan further enhancements to Ehcache to roll in the Terracotta Hibernate provider so that Grails users can experience the Terracotta Scale Continuum by simply making config changes in ehcache.xml.
Note that earlier versions of Grails also ship with the Ehcache library and it very quick and easy to configure it. See the documentation.