I got rather confused today when trying to log in with GH and being told 'your username is available', hang on.. what? I was sure I had an account on this site already, even went into my emails to find notification messages and reference what address they were sent from. Eventually found the announcement post riiight down the bottom.
Anyway: It wasn't obvious to me the site had been 'reset'. Any chance of a banner on the login / register dialogues telling returning users that?
Edit: or perhaps pin the announce post.