I navigate the web and my computer by keyboard as much as I can (mice are for kids). That means I "tab" around web pages to enter data such as usernames and passwords. There are few things in life as annoying as web pages that do not follow tab ordering standards.
Correct flow is tabbing from username field to password field, then to the remember me checkbox, then to the "submit" button. That allows me to enter my info in the fastest manner possible, with the least nuisance. I'm blown away when a web form uses some other (usually random) tab ordering; c'mon!