This is the gruntfile that powers gladdy.co.uk. It's for the blog post here: http://www.gladdy.co.uk/blog/2014/04/13/using-uncss-and-grunt-uncss-with-wordpress/

gruntfile

module.exports = function(grunt) {
  grunt.initConfig({
    pkg: grunt.file.readJSON('package.json'),
    
    uglify: {
      options: {
        sourceMap: true,
        sourceMapIncludeSources: true,
        sourceMapIn: 'js/app.coffee.js.map'
      },
      compile: {
        files: {
          'js/app.js': [
            'public/components/modernizr/modernizr.js',
            'public/components/jquery/dist/jquery.js',
            'public/components/foundation/js/foundation.js',
            'public/components/jquery.smooth-scroll/jquery.smooth-scroll.js',
            'public/components/WOW/dist/wow.js',
            'js/custom_retina.js',
            'js/app.coffee.js'
          ]
        }
      },
      minify: {
        files: {
          'js/app.min.js': 'js/app.js'
        }        
      }
    },
    
    coffee: {
      compile: {
        options: {
          sourceMap: true
        },
        files: {
          'js/app.coffee.js': ['coffee/**/*.coffee']
        }
      }
    },
    
    sass: {
      options: {
        loadPath: ['public/components/foundation/scss','public/components/bourbon/dist','public/sideload/animate'],
        sourcemap: true,
        quiet: true
      },
      dist: {
        options: {
          style: 'compressed'
        },
        files: {
          'css/app.cmin.css': 'css/app.clean.css'
        }        
      },
      dev: {
        options: {
          style: 'expanded'
        },
        files: {
          'css/app.css': 'scss/app.scss'
        }        
      }
    },

    watch: {
      config: {
        files: [ 'Gruntfile.js' ],
        options: { reload: true }
      },
      
      grunt: { files: ['Gruntfile.js'] },

      images: {
        files: 'img/**/*.{png,jpg,jpeg}',
        tasks: ['imagemin:production'],
        options: {
          livereload: true
        }
      },

      vectors: {
        files: 'img/**/*.svg',
        tasks: ['svgmin:production'],
        options: {
          livereload: true
        }
      },

      sass: {
        files: 'scss/**/*.scss',
        tasks: ['sass:dev'],
				options: {
					livereload: true
				}
      },
      
      coffee: {
        files: 'coffee/**/*.coffee',
        tasks: ['coffee:compile','uglify:compile','uglify:minify','jshint'],
        options: {
          livereload: true
        }
      },
      
			js: {
				files: ['js/*.js'],
				tasks: ['concat','uglify:coffee','jshint'],
				options: {
					livereload: true
				}
			},
			
			php: {
				files: ['**/*.php'],
				options: {
					livereload: true
				}
			}
    },
    
    

		// JsHint your javascript
		jshint: {
			all: ['js/app.coffee.js', '!js/modernizr.js', '!js/*.min.js', '!js/vendor/**/*.js', '!js/html**.js'],
			options: {
				browser: true,
				curly: false,
				eqeqeq: false,
				eqnull: true,
				expr: true,
				immed: true,
				newcap: true,
				noarg: true,
				smarttabs: true,
				sub: true,
				undef: false
			}
		},

		// Image min
		imagemin: {
			production: {
				files: [
					{
						expand: true,
						cwd: 'img',
						src: '**/*.{png,jpg,jpeg}',
						dest: 'img'
					}
				]
			}
		},

		// SVG min
		svgmin: {
			production: {
				files: [
					{
						expand: true,
						cwd: 'img',
						src: '**/*.svg',
						dest: 'img'
					}
				]
			}
		},
		
		exec: {
      get_grunt_sitemap: {
        command: 'curl --silent --output sitemap.json http://gladdy.local/?show_sitemap'
      }
    },
    
    uncss: {
      dist: {
        options: {
          ignore       : [/expanded/,/js/,/wp-/,/align/,/admin-bar/,'.swing'],
          stylesheets  : ['css/app.css'],
          ignoreSheets : [/fonts.googleapis/],
          urls         : [], //Overwritten in load_sitemap_and_uncss task
        },
        files: {
          'css/app.clean.css': ['**/*.php']
        }
      }
    }
		
  });

  grunt.loadNpmTasks('grunt-contrib-sass');
  grunt.loadNpmTasks('grunt-contrib-watch');
	grunt.loadNpmTasks('grunt-contrib-jshint');
	grunt.loadNpmTasks('grunt-contrib-imagemin');
	grunt.loadNpmTasks('grunt-contrib-coffee');
	grunt.loadNpmTasks('grunt-contrib-uglify');
	grunt.loadNpmTasks('grunt-svgmin');
	grunt.loadNpmTasks('grunt-notify');
	grunt.loadNpmTasks('grunt-exec');
	grunt.loadNpmTasks('grunt-uncss');
	
	grunt.registerTask('build', ['coffee:compile', 'uglify:compile', 'uglify:minify', 'jshint', 'imagemin:production', 'svgmin:production']);
	
  grunt.registerTask('default', ['sass:dev', 'build', 'watch']);
  
  grunt.registerTask('deploy', ['exec:get_grunt_sitemap','load_sitemap_json','uncss:dist','sass:dist']);
  
  grunt.registerTask('load_sitemap_json', function() {
    var sitemap_urls = grunt.file.readJSON('./sitemap.json');
    grunt.config.set('uncss.dist.options.urls', sitemap_urls);
  });
}

Has anyone solved the Fatal error: PhantomJS: Cannot open about:blank problem?

Yes, me. And there is already an issue for that: uncss/uncss#150

Mine is "Fatal error: promise is not defined" on uncss:dist ? I've search the issue page on giakki and addyosmani, but i cant seem to find anyone having my error.