i think that operating on the default assumption that Craft is for 'showing off' works rather well, and people who want a critique could ask for it when posting to Craft.

optionally, why not check the poster's home node for mail, and send 'em a private critique rather than a public one, so if the ego gets shattered, it's still within the privacy of the home/cube/whatever.

criticism is great - when it's expected. and someone who posts code and writes 'l00k itz k3wl d00d' probably doesn't really want to have errors pointed out -- even if they're deserved.