Signing into a site that you have already registered with should be a smooth experience, but I've recently been frustrated by my own lack of foresight. I have three different email addresses that I use to sign up for various services on the web. I have a Yahoo address that I've had forever, a Gmail address, and my Six Apart address. Unfortunately, I haven't been as careful as I should have been about which address I use to register and I sometimes find myself having to try each of those addresses (and a couple of different passwords) in a frustrating attempt to login to sites that I visit relatively often.
This is a case where the assumption has been made that people know their email address (which is usually a pretty solid assumption), but in my case I've created friction for myself by not using the same email address every time.
It's my own fault, I know, but there is a way that sites can help me with this problem: tell me whether the email address is wrong or just the password is wrong. If the email address that I've entered exists on the system don't just give me the generic "Login is incorrect" message. The error messaging should state either "This email address does not exist on our system" OR "The password you have entered for this email address is incorrect." I know that would make my life a little easier.
