If you want no smilies in your blog, you’d better go to Settings>Writing and make sure this option isn’t checked:
“Convert emoticons like :-) and :-P to graphics on display”
If you do want smilies, and have this option on, you may occasionally run into trouble: most character combinations for smilies are safe, but there’s the unfortunate case of the “8)” combination (for the smilies you can use in wp.com blogs see here). One might very well want, say, the year 2008 in parentheses, and instead end up with 200 plus a smilie with black glasses (supposedly meaning “cool”).
Solution one, enclose the parenthesis in span tags:
Solution two, write the html code for the parenthesis:
(Both of course in the html post or page editor.)