It'd be more interesting to allow some sort of optional rating system which feeds into something like a gaming matchmaking system. People who consistently send out good reviews will get a rank of "A", for example, and be matched to others with similar rankings.
That way, even low-quality posts ("i liek that u have a logo") can be accounted for, without treating them like spam. As the reviewer becomes better at reviewing, they will see an increase in their ranking and better reviews.
Sure. Better to assume it's ok and have a "flag" option, though. On the contrary, it'll put too much of a burden on the submitter and if they fail to approve your comment it won't count.
Perhaps submitter should be able to score feedback as helpful or not, so people can't spam asdf on every site to gain "credits"?