[vxxzy]

This is a terrible idea. At this rate, you're just handing out your data! It is a matter of practicality and security. When someone enters a username and password, you do not know who may be on the other end. Telling them that the username is correct but the password is wrong puts an attacker one step closer to gaining access.

[azurelogic]

Came to the comments to say this. Glad to see I'm not the only one thinking it.