The only project I've yet been involved with that made use of a DSL was focussed on providing telecom services.
Allowing operators to visually design a service by selecting, interconnecting en configuring service building blocks, and exporting such a model to an XML-based DSL.
The Java-based service delivery platform would would read and interpret those service definitions and translate them to their runtime Java equivalents.
Build a man a fire, and he'll be warm for a day. Set a man on fire, and he'll be warm for the rest of his life.
As I understand it the Rails framework (of Ruby on Rails fame) is actually a DSL for building web sites in Ruby. If that's true the I strongly suspect that Grails is a DSL for building web sites in Groovy - the dynamic language with a simplified Java syntax that works well with Java and runs on the JVM.
SCJP, SCJD, SCEA 5 "Any sufficiently analyzed magic is indistinguishable from science!" Agatha Heterodyne (Girl Genius)