gistfile1.js

// IE also doesn't set the accept headers correctly, so you have
// to request a file with the right extension (.js, probably). 
// If you're not using one of the ruby remote form doodads, 
// you'll want to ensure the form is sent to /widget/69.js 
// and not the default /widget/69 :

// make forms do remote requests
jQuery.fn.submitWithAjax = function(){  
  this.submit(function () {  
    // Amend the URL for submitting this form to have a .js extension
    // Otherwise those dorks using Internet Explorer will get a 
    //    Security Warning - File Download
    // and no remote form processing.
    $.post($(this).attr('action')+".js", $(this).serialize(), null, "script");

    //
    // On submit, set the button to have the 'spinning' class -- 
    // which I define to 
    //   .spinning { background: #ccc url('/images/u/spinner-sun-28.gif') no-repeat right !important; }
    // using 
    //   http://assets3.infochimps.org/images/u/spinner-sun-28.gif
    // (see http://www.ajaxload.info to get your own.)
    // 
    // Your response will want to use a similar recipe to 
    //   $('<%= selector_for_the_form_what_called_us %>').find('input[type="submit"]').each(function(){ $(this).toggleClass('spinning', false); });
    // on the buttons within the form.
    //
    $(this).find('input[type="submit"]').each(function(){ $(this).toggleClass('spinning', true); });

    // Don't follow the link to load a new page
    return false;  
  });  
};

$(document).ready(function(){
  // Have AJAX forms ask for JSON in the headers
  jQuery.ajaxSetup({
    'beforeSend': function (xhr) {xhr.setRequestHeader("Accept", "text/javascript")} 
  });
  // Have all remote-classed forms submit AJAX
  $('form.remote').submitWithAjax();
});