I have to offer that I disagree with Thumper's rule. I always try to offer a review for any story I read. If it is good or bad, I try to let the author know why. Of course, I end up pissing off a few authors here and there, but they know why I liked or didn't like their story. If they are an author who is actually interested in improving they will take comments at face value - as honest critisim meant to aid in future writings. If they just want praise they tend to react in a less than stellar manner.

One thing I always try to do, when one of my stories gets a negative review, is to review the reviewer. That is, I check the previous reviews they have offered. If they consistantly flame stories or tend to review bad stories with praise I try to ignore the review. If, on the other hand, they consistantly offer thought out and considerate reviews I tend to pay close attention to the good, the bad and the ugly of their review.