Quantum cryptography is a strange beast. The first commercial solutions, for instance by Quantique ID, are already available. And they are already hacked. Researchers of the Norge Quantum Hacking group have succeed to succesfully eavesdrop communications.
Of course, the vulnerability was not in the concept of quantum cryptography itself but on some technological loopholes. As usually, weakness comes from implementation. They present a nice gallery of pictures illustrating the material and the methods used by the exploit.
It is not the first exploit of this team. See Cracked Quantum Cryptography?