I just discovered that if I go to http://groups.google.com enter a profane search term (think Carlin's 7 dirty words among others), I am immediately returned to the main Google Groups page upon clicking the search button. This also happens when I point my browser to a URL constructed to search for a profane term, e.g. http://groups.google.com/groups/search?q=f**k&qt_s=Search+Groups (replace the asterisks with the obvious letters).

For the record, yes, Google has been censoring Usenet posts* – not sure about your particular tries, though. Do you have SafeSearch enabled or disabled?

* http://blogoscoped.com/archive/2006-06-14-n72.html

Strange, i get the same result.