Placeholder polyfill (requires jQuery and Modernizr).

placeholder.js

// input placeholder polyfill
if(!Modernizr.input.placeholder){
    $('[placeholder]').focus(function() {
        var input = $(this);
        if (input.val() == input.attr('placeholder')) {
            input.val('');
            input.removeClass('placeholder');
        }
    }).blur(function() {
        var input = $(this);
        if (input.val() === '' || input.val() == input.attr('placeholder')) {
            input.addClass('placeholder');
            input.val(input.attr('placeholder'));
        }
    }).blur();

    $('[placeholder]').parents('form').submit(function() {
        $(this).find('[placeholder]').each(function() {
            var input = $(this);
            if (input.val() == input.attr('placeholder')) {
                input.val('');
            }
        });
    });
}