I was reading this Salon.com article that I found via Editorial Ass (thank you, moonrat!) and after commenting on moonie's post, it got me to thinking about the value of critique.
There's tons of resources on the web about the value of criticism and the difference between the positive reinforcement kind and the negative kind. I'm not going into that here simply because it doesn't matter so much to my own thoughts.
Criticism is valuable. There's no question about that. It's only through criticism of our work that we can grow and change as writers to become better than we were when we started. God knows I'm not the same writer I was at age 15 (which is good because I wrote some truly awful stuff then). The criticism I received made me grow in my storytelling, and in my execution, and in my characterization. Being told what's working and what's not working improves the story as well as the writer, which should be our key concern as storytellers -- what works and what doesn't.
However, criticism needs to be detailed. Saying "You need to slow it down" means nothing without pointing out where the story goes too fast. Saying "I don't like it" is similarly unhelpful if you can't innumerate why you don't like it (unless it's the genre and not the story, which means your critique has less value than someone who does read said genre).
Anyway, the Salon.com article says that "refusing to comment" is a good way to get around the thorny issue of dealing with not wanting to injure a writing friend's ego. Which I do agree with somewhat. But only in certain cases.