(Prompted by the discussion on this post.)
As a user-moderated question and answer site, the decision of what sorts of questions are and are not allowed is obviously up to the users themselves. However, since most user-moderation tasks require large amounts of karma to exercise, we are currently not at a stage where the users themselves have enough power to prevent abusive or off-topic posts from flooding the board.
As such, it is up to the designated Moderators (Al Ummat, NesreenA, Jenny_ and goldPseudo) to ensure the site remains viable until the userbase can build up enough karma and site experience to manage things in a more democratic fashion. One significant part of our duties is to ensure that posts follow the rules (as laid out in the FAQ).
It has been pointed out the the matter of deciding whether or not a question is "too subjective" is in and of itself subjective; what one Moderator decides is a problem could be seen as perfectly fine by another, and I agree with the concern this raises. Unlike the regular users, Moderators have the ability to unilaterally close and delete any post that they don't like. When the userbase develops to a point where it can handle the user-moderation tasks, this will not be as much a problem and the Moderators would only need to be called in to handle exceptional situations.
But right now, we're all you have.
Above all else, this is a site for the users. So I'm throwing this question out for both the Moderators and the users themselves.
Under what circumstances should the moderators use their powers to close questions?