So…if I terminate a sentence with a smilie, should I add a period? When I do, it looks like my smilie has a beauty mark, or forgot to use its napkin.
My IMHO…a smilie shall henceforth be treated as a distinct grammatical punctuation object, with all rights, honours and privileges bestowed thereupon, and not as some inline meta-editorial subscript.
Well, since a smiley is not a part of “accepted” grammar and punctuation, all the rules get thrown out the window, if you decide to use one.
FWIW though, when I add a smiley, I don’t use a period. When I need to use an exclamation mark, I’ll use it at the end of the sentence, then add a smiley after the exclamation mark.
I usually end my sentence with the appropriate punctuation, then add the smilie. 
What about when you want to put a smiley at the end of something parenthetical (like this :))? That’s the one I always struggle with. Although it’s not much of an issue when the smiley is replaced with an icon (like this :)).
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Make a sentence, then add Smiley afterwords, with a space. ;->
(and never within a parenthesis) ;->
(unless, you have words :-> in between) 