I get occasionally teased about how much I use smileys and emoticons in my online chats... and yet I wonder why they don't get used more often. How many times have you had a conversation with someone and saw something completely offensive, responded in an appropriately pissed off way, only to have them say they were kidding? How were you supposed to know?
Online conversations... words on a screen... are more subject to interpretation than almost any other form of conversation today. You don't have the benefit of a complete dissertation to fully understand the perspective someone's coming from... and you don't have the benefit of inflection, tone, expression, or body language. You're stuck inferring exactly what this person meant when they made that snippy, bitchy comment. Were they kidding? Were they serious? Was it the wrong window? Were they being sarcastic? Sociology says we'll pick the one we're most concerned about (usually the negative one) and jump to conclusions. Sucky.
In a world where "it's not what you say, but how it's said", a medium like this, that's focused exclusively on conveying words and sentences needs a little more "how" added to it. When you're talking to me, you usually know if I'm joking, smiling, laughing, or just plain being a bitch. You can imagine the facial expression as you read the words because there's a little picture or icon or something behind the sentence to lead you in the right direction.
In a world where misunderstanding causes people to die, and where we talk more with they keyboard then in person, a little extra effort to help people understand us is probably exactly what's needed.