I have to agree with Anonymous51. I don't normally do this, but...I'm going to kick in my two-cents on this subject.
I have (as I suppose we all do) a personal rating system, where if I don't like a post...then I just don't rate it. You see, if I can't say something nice...I try not to say anything at all.
Now, if I do like something I'm reading - even if only so much as a 5 or 6 in my head - I leave a 10 as encouragement to the writer...and as a quiet little "Fuck You!" to the dickish boogyman "Mister One" who pops onto the board now and again and leaves his droppings all over the place. You know what I mean. You see a whole row of low reviews and you just know he/she has been here.
Me personally, A low review means that someone at least took the time to pan something I worked hard on. Composition is torture for me, and most every post I've ever made on this or any site was the result of an hour or more of writing, rewriting and correcting. What discourages me is having no rating at all. A low rating means someone doesn't like it, and I can accept that. A "0" means nobody cares ;>)