In the coming release of CakePHP (RC6) there are some changes in the aforementioned functions. The changes in Session->flash() could break existing code as the function signature has changed (but I think most people use this function without parameters). The old signature was:
function flash($css = 'message', $return = false)
And the new signature is:
function flash($key = 'flash')
The signature of Session->setFlash() has changed, too. Some new parameters were added. So the new signature is:
function setFlash($flashMessage, $layout = 'default', $params = array(), $key = 'flash')
$layout allows you to specify a layout used for the flash message, and with $params you can send data to that layout. The $key parameter makes it possible to store different flash messages in the session. You retrieve them with the new $key parameter of Session->flash().