Doubtless this topic will rage for a while so here's my personal view…
SIC doesn't directly effect any of your sense, but instead 'suggests' things for your brain to interpret as it will, much as we each have individual interpretations of things we see, feel, smell, touch and hear on a daily basis. While we all encounter roughly the same things, the exact thoughts and sensations stirred in each person could be subtely different. With the SIC, this 'stimulation' occurs in what you would basically consider to be your imagination.
If you 'talk' over your SIC, the words are 'formed' in my mind, but wether it's your voice I 'hear' depends on how well I know you, otherwise, my mind attempts to fill in the gaps. I don't physically hear your voice, but rather I get the sensation that I would if I imagined you saying something, I place the familiarity of your voice with your words. If you 'broadcast' the smell of rotting cabbages, I receive that 'thought' and -only- the thought, making of it what I will, mentally perceiving the smell of rotten cabbages.
Someone will probably say something about 'SIC terrorism', forcing images and thoughts into someones mind. This can't be done, coz the SIC doesn't have that kind of suggestive power, it would have no more suggestive power than someone standing infront of me and saying certain things or doing certain things making me no more effected by a given thing on the SIC than I would be if the same thing were described to me face to face. I could SIC *smiles* and you would get the suggestion that the sender was happy etc. And I can basically ignore any given thing, simply choosing to ignore it, much as you might choose to ignore someone who's conversation disinterests you.
By that rational, anything in a SIC broadcast is totally abstract, make of it what you will. It works in the nature of the game, since text, even in fancy ASCIII patterns, conjours up images probably unique in each of use same as we all picture what we read in the game differently.
I'd also say this would be the easiest format to integrate into the game. It's basically impossible/impractical to police what people say/type on the SIC. Screaming at people for typing *smiles* *hugs* 8) etc is never going to work. While personally I don't like to see smileys, I deal with em, but *smiles* *tickles* *claps* I find generally acceptable.
Basically I consider it nothing more than a subconcious ICQ.