I think mentioning the username and email ID is a lot more preferable - and safer. I'm not as concerned about my email getting hacked (in which case, I have bigger problems) than my password being up there in plain text. Most of us sign up for more things than we can remember individual passwords for; many of us probably use a set of few passwords across sites - with our own rules for what's used where. The fact that any person can assume a reasonable degree of password reuse and try my password on (say) Gmail, etc is very disturbing.