I personally won't ever use Medium because it deprives the author of branding and recognition.
If nothing else it sure makes posts from Medium very annoying on HN because I can't actually tell which blogger's post I'm going to read until I click the link (primarily read on iPad so no hovering).
Besides, on the rare occasion I have read an article on Medium (I don't anymore) I could never remember the author. It's all just the faceless Borg.
For anyone thinking of using Medium, don't do it. It's like giving your work away for free, and for no recognition.
Not sure how they will handle open publishing.