Ways to Simplify 'Sign In'

The article quite well describes some of the valuable features of a good login UI.<p>The login page is (often) the first place a user encounter your site. If that page creates a sense of repulsion in the user or forces him to struggle, the user is probably left with a feeling that your site is against him. That's not something you want.<p>Its not difficult nor time-consuming to implement a proper login UI. However, surprisingly many sites don't pay enough attention to it.

I've often wondered this myself when designing login forms, but doesn't identifying which field failed expose a security issue? A malicious user could use the feedback to determine if accounts exist or not. This seems like a concern to me.