On the rare occasion that I have had something to complain about worth more than just casual griping I have taken my complaint directly to the airline's Customer Relations office and supplied them with a link to their specific forum at FlyerTalk. I've done this twice with UA.

There are some valuable customers posting here. In United's case, lots of Premier Execs and 1Ks. Not all of these posts are negative either. Most importantly, it's a great site for an airline to monitor to get a pulse on its most frequent flyers.

As for those that seem to have a vendetta, I've always felt that a valid complaint will stand on its own merit, even if it comes from one with "a vendetta". In any event, I often get more out of other poster's responses to the vendetta holder anyway, especially if their complaint is groundless, so I say let 'em post!