I guess it's impossible in advance of leaving a comment or ranking to say who enjoys constructive criticism, and who does not. Ideally, if someone doesn't want any, they shouldn't allow for rankings or perhaps even comments, but I know that's not really how it works in the real world. I'm one of those crazy folks who IM's thank you notes to those who leave criticism for my gallery postings. I can't think of a single time when "this needs work" comments were abusive, although I know that there are inconsiderate people as well as "trolls" out there. I look at it this way: If I leave criticism, I note what's strong and good about the image first, and try to be polite and specific with the critique. Then if the artist takes offense, I have nothing to feel guilty about, and will know not to critique the person again. I can't say I've ever been annoyed by overly praiseful comments, but there have been times when I've posted a work that clearly had flaws, and was baffled that it got an "excellent" rating. I take the overly positive comments as encouragement to keep working, just the same as the criticisms. :-)