“If you wouldn’t want it written about you, don’t write it about someone else. If you wouldn’t approve it in your comments section, don’t write it in someone else’s.”
Seems to me this would also apply to message boards/forums.
This is sound professional advice, for those of you looking to brand yourself or your business. It's also sound human-type-being advice -- you'll be a better person if you don't "Turn to the Dark Side" and allow yourself to become a flame-happy Troll.