I do not like the idea of a specialized critique forum. Below are my reasons, my counter-suggestion is at the end.

A proper art thread contains a mixed back of responses and opinions about the artwork, it is what makes it interesting and valuable. Censoring genuine feedback in the Art forum will make the threads there pointless. People may fear negative feedback, but look at it the other way:
What's the value of praise if you know people are not allowed to post anything else?Conversely, a specialized critique forum always strikes me as somewhat pretentious in the gfx-forums that have it. Also, it might make people feel obligated to actually deliver more comprehensible feedback than they otherwise would. Which would be great if the end result is usually that they do not post at all - when they would otherwise had brightened the artist's day with a simple but heartfelt line. Delivering a proper critique is an art in itself, not everyone has the time to do that at every turn. Some also wouldn't feel confident enough in themselves to do so.
Another reason for not having a specialize critique forum has to do with what art to put there. Such a forum easily becomes the realm of "non-finished" work (where "finished" work goes into the Art section). At least for me personally, I don't know how many times I've thought my art was "finished" only to have to go back and redo parts of it after having my eyes opened by good critique! On GimpTalk I've gotten good feedback on art in bumped threads years and years after making it. I don't think I would never feel confident enough to say "noone has anything more useful to say now" and post my work into a non-critique-allowed art section.
In my view,
not wanting critique is the exception. I can see cases where not allowing it can be warranted. Cases I've seen are when the artist is in a personally sensitive state or is making some art just to "vent" some real-life issues. In such cases it would be fair to everyone to be able to clearly mark the artwork as a not-open to critique.
In a similar vein as paynekj above, but without going to a full new forum, I suggest a check button when creating new threads in the Art forum. It could for example say "Please do not critique this work". New posters in a thread could be notified of this fact (maybe even by a pop-up) and breaching of this request would be modetated.
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Griatch
PS: I voted "Keep things the way they are" in the poll, but there should really be an "Other - I explain in the thread" option for polls like this.