I should think that the title and summary are enough here, but I'll flesh this out a bit:
Since we all hate it when people shout online, or in messages, because they're too stupid to realize that caps mean shouting or mental feebleness, I propose that computer OSes have a little popup that appears
whenever more than three words are strung together in all caps. It could say something like, "You seem to be typing in all caps, which means emphasis or shouting. Please use proper netiquette" or something like that - the warnings, of course, could be determined by whoever writes the OS.
This alarm would occur whenever someone uses one of the OS's recognized internet-use programs - IE, Mozilla, Opera, Outlook, Rhapsody (or whatever that one's called), AIM, MSN, et cetera. And it would only pop up once per program instance - so if you have IE running in multiple windows, it'll only pop up once, and not pup up again until you close IE, and then restart it.
If it even helps one person change their habits, it's worth the coding time, as far as I'm concerned.
EDIT: It should be noted that similar alarms do exist on some PHP bulletin boards. Not this one, though...*cackle*