I just downloaded the new Mountain Lion, finally. One of the biggest new things is the cool little native notifications akin to growl. I thought it would be cool to get a nice notification when my "grunt watch" task finished. First things first. You need to install terminal-notifier. This allows you to interact with the native OSX notifications system.

There is a ruby gem and a standalone ".app". Once this is installed, you will need to grab the grunt-growl plugin. There are more instructions there for the terminal-notifier app. Now you will need to setup a new task in your gruntfile:

growl: {
  css: {
    title: 'STYLUS BUILT',
    message: 'css/style.css has been created'
  },
  js: {
    title: 'JAVASCRIPT BUILT',
    message: 'dist/js/scripts.js has been created'
  }
}

Now my watch task looks like this:

watch: {
  scripts: {
    files: ['<%= concat.dist.src %>'],
    tasks: ['jshint', 'concat', 'growl:js'],
    options: {}
  },
  styles: {
    files: ['css/*.styl'],
    tasks: ['stylus', 'growl:css'],
    options: {}
  }
}

You can see that the growl task runs after the initial stylus and javascript watch tasks.