Interesting question. I think the answer is, "not very clearly."

I used to think that words without any of the face-to-face cues and so-called "body language" would demand that writers become adept at conveying exactly what it is they wanted to say - that is, if they had any desire at all to be understood by the majority of readers. Universally, that hasn't been the case, as anyone with a modicum of cognitive power can readily discern. Sometimes a writer doesn't give enough consideration to the characteristics of his/her audience. Less emphasis should be given to supplying emoticons for context. I would be in favor of more emphasis on tightening up syntax and structuring sentences to convey context so that *smirk* and :-) are not necessary.   

Practice doesn't make perfect in every case. But I wonder if online communication has bumped up the overall reading comprehension of internet participants, just a little?   

Message posting, email, etc in its present form leaves lots of holes for the reader to fill in for him/herself. In that sense it's sort of like the early days of radio, another medium that required more active participation from the audience than its successor, television. Radio left the visual part to the listener's imagination, so that each listener fleshed out a mental image and attached it to the voice coming out of the speaker. Without the benefit of a photograph or digital image, it is much the same for the readers of people who are composing online messages.