Having been an experienced admin and moderator of some big sites... I have to say the pros outweigh the cons.
Sure, you may see it as "incitement to complain"... but people are going to moan about stuff anyway.
This way, you can keep it focused in one place, easier to monitor and when people start ranting elsewhere on the forums, you can move their post.. or direct them to the complaints area... and stop the bad vibes spilling into other forum areas.
Segregating the negativity from the other threads helps to make those other threads better and a more enjoyable, positive-minded read.
Additionally, it also gives a stronger impression that you guys accept and understand there will be complains about things.
Google went for the 80%... because you'll never keep 100% of the people happy!!! -- and it's true... there will ALWAYS be complaints... at least this way they can shifted into the relevant area and removed from threads where they have a venomous effect on the dialog there.
Now... it's down to the users/players/testers... to use their maturity and common sense to try to make the best of this area by remembering to be constructive, offer alternate ideas and to be understanding...
The devs/gms/moderators have extended an Olive Branch... and we'd be idiots to snap it off.
Complaining, debating, etc. is fine.... but getting personal and insulting people or implying things about people who volunteer their time to selflessly contribute to the community are not good at all. I sincerely hope we all make use of this forum area in the best possible way.
Thank you.
[ Edited for language. --Karyuu ]