MS Word Spelling Checker
A friend of a friend of mine once was typing up the tracklisting of an (Oasis, if my memory serves me correctly) CD in Microsoft Word. One of the tracks was called "f***ing in the bushes" -- but originally with the letters U, C and K in place of my friend's friend's modesty-stars.
What was interesting was Word's list of suggestions for the "mis-spelt" word. These included "face-lifting" and, probably with an ironic ring of truth for some people, "fact-finding" ! As in, "The minister has just returned from a f***ing mission to Thailand."
Interestingly, further experiments showed that Word treated correctly-spelt swear-words as correctly-spelt, but never offered them as suggestions for mis-spelt words -- so it must be keeping track of which words are or are not considered fit for use in polite company.
That gives me an idea for a hack which would be much more phun than simply popping up pr0n sites or redirecting web searches to competitors' sites .....