HTML5 placeholder fallback for browsers that don't support it, implemented in jQuery. NOTE: This will not work for elements added to the DOM after initial load

jquery.placeholder-fallback.js

// Function to test for attribute support
function elSupportsAttr(el, attr) {
  return attr in document.createElement(el);
}
// does input support placeholder? if not, add fallback
if ( !elSupportsAttr('input', 'placeholder') ) {
  $(document).ready(function() {
    // everything with placeholder attr
    $('[placeholder]').each(function() {
      $(this).val($(this).attr('placeholder'));
      // remove on value focus
      $(this).focus(function() {
        if ( $(this).val() == $(this).attr('placeholder') ) $(this).val('');
      });
      // add value on (empty) blur
      $(this).blur(function() {
        if ( $(this).val().length == 0 ) $(this).val($(this).attr('placeholder'));
      });
    });
  });
}