continuous deployment of a grails app
Check the nojars argument for the war task: http://www.grails.org/doc/1.3.7/ref/Command%20Line/war.html
This way you can place all your .jars (which are usually the biggest files inside a .war) in some other directory on the server and just reference that directory in your Jetty classpath.
Or you could write a shell script to explode the .war file (after all it's just a regular .zip file), add the compiled classes and then re-package it.
You could try using CloudBees to do continuous delivery releases. They also use deltas to upload your changes, and deployments don't affect the user experience at all.
An easy to use plugin is available to make the process seamless from within your Grails app and in a Jenkins build. I've written a blog post about how to get it all working easily.
Maybe the Cloudfoundry Micro Cloud is an option, a deployment just transfers the deltas and not the whole war file.