I love receiving real critique; I have received many excellent suggestions which I have incorporated (to the best of my limited abilities) from that point onward.  I hope it's helping me improve.  It's also nice to get some "wow!" compliments, as it makes me think that I am getting better and encourages me to keep on working.   I'm often surprised at the shots that get a big response when I didn't feel it was particularly good, and I try to find what worked for people so I can learn.  And I'm also often surprised that some of the shots I thought were great didn't get much response.  I do find it annoying to get the "canned" comments which seem to me to mean that someone hasn't really looked at the image.   I have given some critical suggestions, but not as often since I don't like to complain if I can't give advice as to how to fix the problem, and I don't know enough.  I have used sitemail for a few of the most critical suggestions.