The UK's GCHQ delivers a brutally blunt assessment of quantum key distribution:
QKD protocols address only the problem of agreeing keys for encrypting data. Ubiquitous on-demand modern services (such as verifying identities and data integrity, establishing network sessions, providing access control, and automatic software updates) rely more on authentication and integrity mechanisms -- such as digital signatures -- than on encryption.
QKD technology cannot replace the flexible authentication mechanisms provided by contemporary public key signatures. QKD also seems unsuitable for some of the grand future challenges such as securing the Internet of Things (IoT), big data, social media, or cloud applications.
I agree with them. It's a clever idea, but basically useless in practice. I don't even think it's anything more than a niche solution in a world where quantum computers have broken our traditional public-key algorithms.
Read the whole thing. It's short.