JS error(s) with Media-7.x-2.0alpha4 and CKEditor
For CKEditor: At first glance, it seems that commenting out the following lines in media/modules/media_wysiwyg/js/media_wysiwyg.format_form.js allows the button to work again... 

      // Get all the values
      var ret = {};

      $.each($('#media-wysiwyg-format-form .fieldset-wrapper *').serializeArray(), function (i, field) {
        ret[field.name] = field.value;

        // When a field uses a WYSIWYG format, the value needs to be extracted.
        if (field.name.match(/\[format\]/i)) {
          field.name = field.name.replace(/\[format\]/i, '[value]');
          field.key  = 'edit-' + field.name.replace(/[_\[]/g, '-').replace(/[\]]/g, '');

//          if (Drupal.wysiwyg.instances[field.key]) {
//            // Retrieve the content from the WYSIWYG instance.
//            ret[field.name] = Drupal.wysiwyg.instances[field.key].getContent();
//            // Escape the double-quotes and encode it to play nicely within JSON.
//            ret[field.name] = encodeURIComponent(ret[field.name].replace(/"/g, '\\"'));
//          }
        }
      });


  return ret;


Be careful though, this is not a permanent solution as you should never hack core.