Have you ever noticed WinXP login screen prompting Caps Lock turned on for your password field?
It is a nice thoughtful titbit that WinXP has provided. Most of the time you unlock and just type in your password without noticing that Caps is on and get your password denied. After trying couple of times you get to notice that Caps is ON. Even you can end up in your account being locked. All these hassles are prevent by this little titbit.
See how a small feature improves usability.