I both enjoy and don't enjoy critiquing other people's fiction work. With my writer friends I enjoy it, because I know them and their caliber personally, and therefore know the work will be good (or at least have high potential) from the outset. I also know that they're not going to hunt me down and staple my ears to the pillow if I don't rave about the first draft. I enjoy watching something rough get polished into something amazing.
With others, it's a little more nebulous. I often critique novels and short stories for people online, either through websites like LiveJournal or through NaNoWriMo's forums. In university I took a class that involved workshopping our fiction. In these cases, it's almost always a toss-up. The problem is not whether or not the work is good; if it is, great, but if it's not, that's what editing is for, so I don't take issue with that. The problem is what happens once the writer gets the critique.
It's not hip nowadays to say you're sensitive about your writing, and for good reason; if someone is honest enough to say they're thin-skinned and don't want heavy critique, I pass the request by. It's probably my fault (and the faults of people like me) that writers are afraid to admit they're sensitive. I see a lot of "bring it on!" and "harsh critique OK" and "I'm bulletproof" in critique requests. Unfortunately, whether they really are is anyone's game.
First, let me just say: I do believe that everyone is sincere when they say they can handle heavy critique. But that's sort of like saying you think habaneros are no big deal right before you pop your hand into the jar and stick a couple in your mouth. (Aside: DON'T DO THIS. Half my family is from Mexico and another quarter from Texas and I wouldn't even do that. Maybe my cousin would, but he blew off his thumb trying to detonate a stump with blasting caps, so I wouldn't trust his judgement.) It's one thing to say you can handle anything, but it's quite another to receive your literary baby back red-penned to high heaven and reeking of the critiquer's disdain.
I know. I always get everything I write read by others — friends, family and strangers, writers and readers — and I am unreservedly bulletproof. I wrote Star Wars self-insertion fanfiction when I was twelve, for goodness' sake; I know the dreck I'm capable of producing and can yet be dead proud of, and I want to get as far away from that as possible. Even so, I always cringe a little when I first get that bullet-point list of things I did wrong. No matter how bulletproof you are, unless you're some sort of literary masochist, it's never fun to see scribbles through that one passage you toldyourself was perfect — the one that, no matter what else was wrong in the manuscript, would shine through and make the reader weep with inadequacy.
That said, it's equally frustrating to spend time on a requested critique only to have the writer "but but but …" every detail. Like I said, I was in a university workshop. I know. The first session, the author took all our criticism (and praise, mind!) in mulish silence, glaring at the ceiling and only speaking to refute or excuse every change we proposed or question we had. This is not professional, but I see it all the time.
As a writer, you don't need to take everyone's advice. In fact, a surefire way to ruin a manuscript is to do exactly that. But you do at least need to consider said advice, and, if you do intend to reject it, why your way works better. Wah they don't understand meeeeeeee is not a valid reason. I've known people who have passionately argued why five comma splices and four split infinitives on one page (in the narration, mind, not dialogue) were vitally important to the plot. I half expected them to argue the typos, as well.
There are two main problems that I see when people send their work out for critique. The first is a lack of distance: many writers toss their books out the door as soon as the ink has metaphorically dried on the computer screen. Still others submit it when they're still writing the first draft. As I said, I'm bulletproof, but I never, ever request heavy critique on in-progress works because it kills the creative part of my brain and switches me over to the editing part. The only time I ask for actual critique on a work in progress is when I'm stalled — and I mean dead stalled — and I know that somewhere in the last ten thousand words I've gone terribly wrong, but I can't tell how far back I need to go back and start ripping seams. Most people who rush out and post that first glorious paragraph in a haze of endorphins and oxytocin stagger back shocked and appalled at the "viciousness" with which people "attack" their work. Often they're too discouraged to continue; in this case, one can usually expect a post from them telling everyone that their discouragement killed their creativity, and everyone should feel guilty. (On the rare occasion I asked for feedback too early, I did this. It was over one word. I still cringe when I think about it, and feel the urge to apologize to the person in question.)
The second problem is that many writers confuse revision with copyediting, and aren't clear when forming their requests. I've received stories and given them back with suggestions on characterization, pacing, missing or gratuitous scenes, and so on, only to have the writer recoil in horror that I'm being "way too mean". After a few back-and-forths it's clear that the writer only wanted a brush-up on spelling and grammar errors. Sometimes the writer was convinced they only needed that brush-up, that the rest was absolutely perfect. At this point I tip my hat, apologize for wasting their time, and get away. Fast.
Because the corollary to number two (and I've been here; we've all been here) is the writer who thinks their work is at final-draft stage, and who only sends it out "for critique" in order to get heaps of praise. They want the oohs and ahhs and the protestations that there is nothing to criticize, only literary gold. The problem is that the sort of people who volunteer for giving critique can sense this, and not all of us are nice (sometimes I'm not — to eye-roller and ceiling-glarer in my university workshop, I definitely wasn't). Some reviewers (and I try not to do this) are extra-harsh to bring the writer down, which is a breach of etiquette in my opinion, but it does happen. There will always be one or two reviewers who fulfill the writer's needs, of course, telling them it's amazing and not to change a thing, and sadly, a lot of writers will just listen to that advice and discard the rest because everyone else is unjustifiably harsh.
Sometimes, though, a writer means it when they say they want real feedback. They want the harsh critique; they want to mould and wrestle their babies into something fantastic, and they're grateful for opinions. Whether they take my suggestions or ultimately decide that I misunderstood or am not the right reader for their work is irrelevant.
The most important thing, if you're asking for critique, is to take it in stride. Sometimes the reader thinks you're brilliant; sometimes he hates your main character; sometimes she thinks your story is boring and not going anywhere. Take a break — or a drink, if that's your thing — and come back to it, if it's too much to go through all at once. Don't expect that all critiques will be nothing but praise. Don't try to please everyone. Don't be afraid to ignore suggestions, but if you do, be aware of what you're doing and why. Don't think you're a horrible and overly-sensitive writer if it stings, because it stings most people. Do compare the suggestions of various critiquers against each other, and do consider their reading preferences when contrasted with your genre.
After you've taken a walk or a bath or eaten some quality chocolate, sit back down with your manuscript, give it a hug, and tell it everything is going to be all right. Then, get to work.