In my experience, `placeholder` polyfills try way too hard, and the results are mixed. Here's mine.

placeholder-polyfill.js

if (!Modernizr.input.placeholder) {
	
	$('*[placeholder]').each(function() {
	
		placeholder = $(this).attr('placeholder');
		
		$(this).attr('value', placeholder).addClass('fakePlaceholder');	
		
	});

	$('form').on('focus', '.fakePlaceholder', function() {
		
		value = $(this).val();
		placeholder = $(this).attr('placeholder');
		
		if (value == placeholder) {
			
			$(this).attr('value', '');
			
		};
		
	});
	
	$('form').on('blur', '.fakePlaceholder', function() {
		
		value = $(this).val();
		placeholder = $(this).attr('placeholder');
		
		if (value == '') {
			
			$(this).attr('value', placeholder);
			
		};
		
	});
	
	$('body').on('submit', 'form', function() {
		
		$(this).find('.fakePlaceholder').each(function() {
		
			value = $(this).val();
			placeholder = $(this).attr('placeholder');
			
			if (value == placeholder) {
				
				$(this).attr('value', '');
				
			};
			
		});
		
		return true;
		
	});

};