I have read somewhere that it is a mark of a poor writer when one has to use smileys to convey humor.
And I always thought it was punishing phrasing.
It is an inchoate cry for liberation, the graphical medium convulvsing to throw off the sullen bonds of text.
I think of smilies more along the lines of mugging the camera or softening a remark.
We make faces when we say something tastes bad--is that the mark of a poor speaker? We smile and touch our friends when we tease them, even though they already know it is all in fun.
Graphical, tactile, textual...we communicate simultaneously in all kinds of ways in our daily lives, duplicating or even contradicting our spoken words with glances and gestures. In online communities we are using text in a relatively new way, more "live", more distributed, more potentially communal; faster and hotter, yet somehow less physically intimate--I tap my keyboard but I caress my books.
Perhaps it is a tribute to the intensity of web communities that we seek those multiply channeled, productively redundant, and more nuanced communications here.
OTOH, me, I just like to make faces.