A quick and simple solution for browsers that don't support the text input placeholder attribute.

html5Placeholder.js

(function ($) {
	$.fn.html5Placeholder = function () {
		this.each(function(index) {
			var placeHolderText = $(this).attr("placeholder");
			if (placeHolderText) {
				$(this).val(placeHolderText);	//set the placeholder text as a text in the input box
				
				$(this).focusin(function() {	//remove the placeholder text on focusin
					if ($(this).val() === placeHolderText)
						$(this).val("");
				});
				
				$(this).focusout(function() {	//put back the placeholder text on focusout
					if ($(this).val() === "")
						$(this).val(placeHolderText);
				});
			}
		});

		return this;
	};
})(jQuery);

This is a JQuery plugin. Use with Modernizr:

    $("input").html5Placeholder();
}