Although there are a few exceptions, I generally try and avoid the use of smilies in my posts <--(see, no smilie here!) for the same reasons you mention above. I'm afraid they will confuse my otherwise carefully crafted (well
usually carefully crafted) prose.
See. The smilie I used above could be self-depricating, embarassed or sarcastic depending on the reader. I include it because I intend the reader to decide for themselves whether my prose is careful or not and whether I'm aware of how careful it is (or not!) In this case, the confusion as to its meaning enhances the message so I include it.

Does this smilie mean laughter, or sticking your tongue out like a school-child teasing a classmate? Just wondering.

<--maybe this means laughter!