[UncleMeat]

Then why aren't you just using old school signature based auth? What does having your public key stored on the ethereum blockchain accomplish?

[Uehreka]

It’s not about storing your public key, it’s about storing your username and the fact that you (the owner of that key pair) exclusively own that username (for any system that federates with ENS).

[Sargos]

Your public key is available to everyone on the internet so anyone can verify your signed message. You can't do that without a blockchain unless a trusted third party is used.