Flickr has developed a reputation as a place where you will only get good comments on your photos. You know, the short comments like “Amazing colours” or “Wow! This is the best photo ever”. Should you also like to receive constructive criticism on your photos, you’re pretty much out of luck unless you build up a group of other like-minded Flickrers. And heavens forbid you should make a constructive criticism on the photo of a stranger; which risks anything from being blocked to being attacked by the photographer’s legion of fans. You might even be labelled, as I was, a negative person that never has anything good to say about anything.
I just read Why Negative Feedback Is A Gift and while it is talking about feedback from a company’s customers, it applies equally well to Flickr. If you are one of the Flickr members that hates receiving criticism on your photos, go and read this article. Then remember, next time you receive a critical comment on a photo, the commenter is not attacking you; they simply care enough to want to help you improve your photography.
craniac's place 
The problem is most people out there cannot take constructive criticism for what it’s worth, learn from it and grow.
Exactly what the article I refer to is saying.
great thoughts there, however I would also suggest that for those who are specifically wanting feedback, and not just a vehicle for showcasing or sharing (which is what I see flickr as), pop in at http://www.photocritique.net/
Its ugly, but its comprised almost entirely of serious photographers (pro or hobbyist) who will critique, AND give advice. I learnt a huge amount while I was posting there…
Thanks for the link Kevin. I’ll check it out.