Well, the discussion about the "kind of categories" missed a very important one: Categories used to group wikipedians by poitical/religious beliefs like [[Category:Muslim Wikipedians]] [[Category:Born-again Christian Wikipedians]] [[Category:Flying Spaghetti Monsterist Wikipedians]] [[Category:Roman Catholic Wikipedians]] etc which are sometimes used to raise voting blocks. The emphasis on "this user is/believes foo" is quite different from "this user is interested in foo". if I recall correctly, categories as the ones I mentiones above are not welcome on wikipedia, but I may be wrong. Can someone else please give me mroe feedback? Maybe previous discussions, statements by jimbo or arbcom, etc... Otherwise, I'm depopulating such categories (which over 95% of them are done via userboxes) and removing them afterwards.