It's a basic necessity of forum/chatroom use IMO (in my opionion).
When you talk to someone face to face, you can tell if they're being humerous or hostile by their demeanor, you can't do that online - hence the use of :-) ("I'm happy") or ;-) ("I'm not being entirely serious") or :-/ ("hmm") face emoticons.
This is ESPECIALLY important IMO when there is a regular online community of people who may be housebound or never intend to meet their online friends IRL (In Real Life) for some other reason.