grunt_growl.js

/* Inside grunt.js file (don't forget to add "growl" as a project dependency) */

grunt.utils.hooker.hook(grunt.fail, "warn", function(opt) {
  require('growl')(opt.name, {
    title: opt.message,
    image: 'Console'
  });
});


/* ... or, since fail.fatal() will stop grunt it seems a good idea to track it too */

var growl = require('growl');
['warn', 'fatal'].forEach(function(level) {
  grunt.utils.hooker.hook(grunt.fail, level, function(opt) {
    growl(opt.name, {
      title: opt.message,
      image: 'Console'
    });
  });
});