It's been mentioned by many (including myself) that people do not leave comments pointing out flaws or suggesting improvements because they are afraid of hurting someone's feelings or have had poor response to having been honest in the past (flaming pm's etc.).

To that, I'd like to suggest when people upload, they are allowed to select the level of critique they would like/are capable of receiving.

"Be gentle with me" - Low
"I can take it" - Medium
"Pin the tail on the donkey" - High aka Hit me with your best shot.

I do not think there should be a "none" category as it would defeat the purpose of this site which is to help artists stretch and grow in a community atmosphere.