It seems like a well adopted web standard that a login form should have a "don't have an account? [Sign up]".
I'm having trouble seeing the rationale behind it. How common is it really that a user clicks on login enters details that are not in the system and then proceeds to sign up via a different form?
We have kind of a special situation that I'm working on where we will do a domain switch. The old user database will not be brought over to the new site so old users might try to log in with their old details. In this case it makes sense (we're going to great lengths outside of the login case to inform the users what is happening).
I'm opting for displaying information about signing up when the login fails. But I've run into an argument with a stakeholder that claims it needs to be a visible link that is always availible. His argument is that "every body else is doing it".
So why should you be able to see an option to sign up when you're entering an area to log in?