application.js

App.ApplicationController = Ember.Controller.extend({
	hideHeader: false,
	observePath: function() {
		if (this.get('currentPath') !== 'index') {
			this.set('hideHeader', true);
			$('#header').slideUp();
		} else {
			this.set('hideHeader', false);
			$('#header').slideDown();
		}
	}.observes('currentPath')
});

gistfile1.txt

{{#unless hideHeader}}
	<div id="header">
		{{partial upper}}
	</div>
{{/unless}}