I post here for several reasons, mostly personal, but I do enjoy the feedback. Even the generic "awesome" or "copy and paste" comments let me know that people have at least been taking the time to view my works. Of course there are the more constructive comments that help me along in my progression. 
 If I post an image and no-one comments, it doesn't discourage me. As other posts have stated, family members and friends usually don't give the best critiques, however, those that come from fellow artists, be they hobbyist or professional, help me see what may not be obvious to me.
 I am a hobbyist but I do take my works seriously, and Renderosity has helped me to get a certain degree of satisfaction by displaying my images. I can stare at my own images and not see what an
objective viewer that has no ties to me may pick up immediately.
 I may not be the best at what I do but the personal satisfaction of my art being seen by those that share my interests is quite gratifying.