Anyone else noticing that the smile icons appear/disappear randomly? Right now as I compose this message, all but three of the smiles are replaced by their underlined word form. Seems to be a quirk in the forum. I wondered why I kept noticing people spelling out their smiles in their messages.

<--- this one works... for the moment anyway.
Not a forum problem as such. What is happening is that the image for the icon hasn't been retrieved when you're viewing the page, so you're seeing the "alternate text" for the image. The problem could be a slow or busy network connection/forum server/your computer/your browser.
Generally web pages load by first retrieving the HTML, parsing it, and then retrieving images/displaying parts of the page as the browser figures out what it has enough information to display. In this case the browser used the alternate text version of the image while waiting for the image to arrive from the server, over the network.
What I've noticed is that in some quotes, the icon doesn't show up it says "wink" or something.
What may be happening in this case is either what I described above or when the person quoted the message, their browser had not yet retrieved the image, so the quote captured the text and not the complete link to the image.
http://www.w3schools.com/tags/att_img_alt.asp :
The required alt attribute specifies an alternate text for an image, if the image cannot be displayed.
The alt attribute provides alternative information for an image if a user for some reason cannot view it (because of slow connection, an error in the src attribute, or if the user uses a screen reader).