The relationship between simplified and traditional characters can be a headache for organizations using both orthographies.
"A number of surveys, such as [Xiandai 1986], have demonstrated that the 2000 most frequent SC characters account for approximately 97% of all characters occurring in contemporary SC corpora. Of these, 238 simplified forms, or almost 12%, are polygraphic; that is, they map to two or more traditional forms."
Nevertheless, it's a task that can one day be done relatively perfectly by a computer. Google Translate can do it for you more or less. But if you are converting a short story or a novel, the task is a little more difficult. That's why I actually prefer to use the Mediawiki converter.
Nevertheless, I don't really know how it works. I have a feeling the SCIM pinyin input tables are used somehow, and the tediously underdocumented non-bijective-mappings between the two orthographies coded for manually. Is that right?