I think Tony makes some excellent points here. I think we do err on the side of saying "great Job" too much but I also completly understand the problem of asking for feedback and then not liking it when you get it.
I would like to offer something though as someone who feels I have learned a lot from really great feedback. Although I always really encouraged honest feedback in my posts, I wasn't always ready to hear it. Well that was MY problem. When I actually got my head out of my ass, stopped being precious and really, really listened to what was being said, only then do I think I learned how to really use feedback and really start to improve.
So, yes it's great to be encouraging and most people here do a top job of that. But I do sometimes think we err on the side of saying "great job" a little too much, although "great job" beats "you suck" any day of the week and twice on Sunday.
My worry is that sometimes people submit something and don't really get much feedback on how to improve it.