Yes, every account at MtGox was "leaked".  Lots of folks have usernames, email addresses (if you had one associated), and the HASHED password.  The only way to break the password is brute force hashing (anyone got a rig for that?).  If you have a strong password, you're probably fine.  If you had a weak password, you're compromised.  If you used that password on an account somewhere associated with either the username or the email address in question, you're probably compromised there as well.

You should probably make it case insensitive. Putting my email in all lowercase tells me "Nope!" but putting it in the same way it is in the database says "Yup!"