The reason this thread was started was my joke after seeing 'bunny(admin)' shouting at players (I don't log the chat to prove, but admins can have it). Nor did I suppose it would be taken that seriously.
My opinion: absolutely no reason to write down rules regulating caps lock usage. Such rules don't add fun or anything to the game. To continue with the joke, let's specify also how many consecutive exclamation marks can be used by non-admins.
Further, caps lock usually associates not with authority, but with childish hot temper. Hence, if I may give an advice to admins, you should better use admin tags in names, and/or (if technically feasible) make admin's chat color-highlighted, instead of shouting with caps.