I'm sure there are a lot of online etiquette (netiquette) rules in Japanese. In English, there are a lot, too. One is this:
'Online Manners - DON'T SHOUT More internet etiquette tips: Whether you're sending emails, chatting online, or using an instant messenger, using ALLCAPS is referred to as "shouting." While it is permissible to occasionally use ALLCAPS to emphasize a point, people find entire sentences written in capitals hard to read. As a result "shouting" online is considered rude.'
THIS IS WHAT SHOUTING LOOKS LIKE. IT IS VERY LOUD. YOU SHOULD ONLY DO IT IF YOU ARE ANGRY OR YOU WANT TO MAKE PEOPLE MAD. Excuse me. I'll lower my voice now.
In the social networking world, it is considered poor taste to send an invitation to friendship without an explanation of who you are or why you wish to become friends.
Even a social networking guru like Tim O'Reilly found it necessary to discuss this: