document.observe('dom:loaded', function() {
  var handleOther=function(){if($F(this).blank()){this.value='Other:';}};
  var clearOther=function(){if($F(this)=='Other:'){this.value='';}};
  $$('input.other-value').each(function(inpt){(handleOther.bind(inpt))();inpt.observe('click', clearOther.bind(inpt));});
});