Why not? Granted, it would cost a little bit of money, but the security and peace of mind is well worth the 25 bucks that a yubikey costs. I know that they can make yubikey work with multiple sites, etc. Mt. gox's key will only work with mt. gox. But, this would solve the phishing issues. I, for one, am in love with the yubikey.. I think every site that is concerned with security needs to have one... Plus, I don't think it's that difficult to implement..