Good critique actually requires more effort than merely typing 'ooh, great', and usually deserves a 'thank you' even if you personally disagree with the remarks. There is no obligation to change anything about your image to suit someone else's preferences, of course, but a second (third, fourth...) pair of eyes can often pick up on details missed due to being 'too close' to an image during its creation. It's rather like having a proof-reader read a piece of writing: the number of times I've missed out a word in a sentence, yet managed to 'read it into' the paragraph when checking it myself! So if you find someone willing to resk a knee-jerk 'don't criticise me!' reaction, try to be nice, even if you think they're wrong (and a year down the line, you may even realise they were right after all). Now that sounds preachy. Sorry, that's not the intention. It's as much a reminder-to-self and a comment to others.