shim for browsers that don't support the html5 placeholder attribute

placeholder.js

setup_placeholders = (function() {
    $.support.placeholder = false;
    test = document.createElement('input');
    if('placeholder' in test) {
        $.support.placeholder = true;
        return function() {}
    } else {
        return function(){
            $(function() {
                var active = document.activeElement;
                $('form').delegate(':text', 'focus', function () {
                    var _placeholder = $(this).attr('placeholder'),
                        _val = $(this).val();
                    if (_placeholder != '' && _val == _placeholder) {
                        $(this).val('').removeClass('hasPlaceholder');
                    }
                }).delegate(':text', 'blur', function () {
                    var _placeholder = $(this).attr('placeholder'),
                        _val = $(this).val();
                    // No need to test for values specific to a particular jQuery version
                    // undefined and an empty string both are falsy
                    if (!_placeholder && ( _val == '' || _val == _placeholder)) {
                        $(this).val(_placeholder).addClass('hasPlaceholder');
                    }
                }).submit(function () {
                    $(this).find('.hasPlaceholder').each(function() { $(this).val(''); });
                });
                $(':text').blur();
                $(active).focus();
            });
        }
    }
})();

.attr('blah') returns undefined in newer versions of jQuery - you can work around this using:

var _placeholder = $(this).attr('placeholder') || ''

https://gist.github.com/3084976

Updated to be friendly to more versions of jQuery. May update for prop method detection too.