People do complain on the boards but usually they didn't complain at the time. Most of the problems people encounter is because they didn't speak up at the time so someone could fix it or get it sorted.
I disagree with this for a few reasons. Granted, as another PP has mentioned, there are some folks who for their own reasons are hesitant to ever voice a complaint (regardless of the restaurant location- WDW or elsewhere). However I think a lot of complaints voiced here on the Disboards would be pointless to make 'at the time'. Take a look at some of the common complaints made here:
1. Long waits to be seated. You've got a 6:00 ADR at XYZ restaurant. There's a big crowd already waiting to be seated. You wait for 30 min and still haven't gotten your table. Do you really think that going up to the podium and complaining is going to get you seated any faster? I'm not saying you shouldn't go up and ask how much longer it's going to be, but demanding to see the manager isn't going to empty a table any sooner.
2. You don't like your table location. Unless the restaurant is half empty or you are prepared for a lengthy wait, I don't think it is reasonable or practical to insist on a different table at most of the WDW restaurants. And aside from the always desired patio table at Rose and Crown, or the tables right against the glass at Coral Reef, I don't even see this as being a factor.
3. Poor service. Your server has 'an attitude'. What are you going to do? "Excuse me miss, but I don't like your attitude. I'd like you to be more Disney friendly please". Or perhaps you should summon the manager and request a more pleasant server? Or the server takes too long to bring your food, drinks, refills, bill. Exactly what are you going to do about it at the time? Get up from your table and hunt her down?
4. The food is poorly prepared. OK, here is where you can do something about it. By all means send it back and have it re-done. Politely, of course.
5. Miscellaneous factors: high noise levels, annoying guests at nearby tables, kids screaming and running around. Absolutely nothing you can do about these things at the time. Sure you can complain to your server or manager. But there's not much they can do about it.
What I am trying to say is that there are lots of things that we complain about when reviewing our dining experiences here on the boards. Very few of these things could have been effectively altered by complaining at the time.