So much word. Learning to take criticism with grace was probably one of the more valuable lessons I learned in art college. It also helped me get better at distinguishing between what was constructive and what wasn't - a professor who pointed out that my proportions or light sources, etc. were off and how I could have done better were being constructive. The professor who told me "it looks like you didn't even try" on a project I'd worked on for upward of nine hours was being a jerk.

Concrit gets tricky in roleplay. I think the How's My Driving things and feedback memes are a good idea, although there's flaws with them (much like many other instances of constructive criticism). Some people fear that they can't give effective concrit unless anonymous posting is enabled, but so many people can be utter jerkfaces when anonymous posting is enabled. I tend to think that since a person is not roleplaying as a career, that they shouldn't have to accept anonymous criticism if they don't want to.