Negative side, it's bound to Mt. Gox so you can't use it as a normal YK on any other site.
Did you try it on http://demo.yubico.com/php-yubico/one_factor.php ?
It is pitty if the key cannot be used outside MtGox (yes, I've read their EULA
AFAIK yubikey has 2 slots for secret key, they can be switched by long tap. I wonder why they removed Yubiko key instead of using the second slot. If they would leave Yubico's secret key then the key could be used on other sites for authentication...