Every day I log into about 10 different accounts to check reports, pay bills, etc.
A good login form should allow the user to do all the data entry on the keyboard. The user should be able to tab 2 times and press return.
Today I counted 4 login forms that break tab order. Azoogle is an example of a broken login form. Banks and credit cards often do odd things as well.
In the example above I use the "tabindex" property to ensure a reasonable tab order. I also like to see the "Need help" or "Lost Password" links or "Remember Me?" checkbox after the submit button.
I'm not saying I'm the expert on usability, but login forms that don't work this way are annoying. Over the course of the year, they probably cost me about 3 minutes of lost productivity due to unnecessary mousing - or about 1/2 the time it took write this blog post...