"For me, I don't comment on pictures unless I feel that I can contribute something to the artist in an effort to help them out with the image or with future art.  When I do that, I also make an effort to point out what I like about the pic too."

That's a great attitude to take, mboncher but sometimes it's just nice to get a "well done". A boost to the moral is just as important to sensitive people. Silence is a killer too, especially in art.