Every three months Windows reminds about changing password. And Windows 7 does in unobtrusive way:
Windows XP shows a dialog box asking whether you would like to change your password now, when you log in or unlock your computer. You have to click a button to continue working. I like the way Windows 7 does it better. Moreover there are email reminders sent in 21 days before your password expires.
Users don’t see such messages at home: Who wants to make oneself change one’s password every three months?
Do you have a password on your home computer?
Have you ever changed it since you setup Windows?