I think feedback really helps everybody. I understand Ron's point about the expertise that some users have. However, all photos make an impression of some sort. The feedback I enjoy giving, or receiving for that matter, are for/from those who think beyond the technical and relate to the photo in a human way. Some of the bestshots may not be the best technically. If you like something and can attempt to explain why, it not only pleases the photographer to hear it, but it improves ones ability to give feedback as well. Compulsory critiquing? I don't think so. If I have the time and inclination I like to write a decent critique/comment. I still love to view the gallery anyway, even if I haven't posted anything myself.
A good question which has initiated some interesting views.