How do I get at the goodies in my Grails Config.groovy at runtime?

In more recent versions of grails ConfigurationHolder has been deprecated.

Instead you should use the grailsApplication object.

grailsApplication.config.grails.serverURL

If in a Controller or Service then use dependency injection of grailsApplication object.
e.g.

class MyController{
    def grailsApplication
    def myAction() {
        grailsApplication.config.grails.serverURL
    }

See How to access Grails configuration in Grails 2.0?