If you know your punctuation has been sloppy, but your friends are ace at fixing it so you think you don't have to bother, then that's just disrespectful. Everyone's time is important. Aren't you busy? Do you have loads of time to write? Or do you squeeze your writing in around a hundred other things the way most of us do?
So, you might think you haven't got time to check the spelling of that difficult word -- and, hey, you know there is a verb "curb", and you've seen the noun "curb" in the latest book you just had sent out from the States, so it must be right, right? Not if you're living in Australia (or Britain for that matter). In Australian usage, the noun is "kerb". You mightn't have time, but if you don't do it, you're taking up your workshopping buddies' time. Some of them are going to have to look the word up. It might take you an hour to fix the punctuation, but if you have ten friends and they're all spending an hour on it, it's not very fair, is it? Trust me: their time is just as important to them as yours is to you. And, if they're not busy looking at all the stuff you know how to fix, they might just have the time to see something more in your story that they otherwise might have missed -- the forest for the trees, and all that sort of stuff!
But what about when you're in the workshop. In the typical Clarion workshop (and many other serious workshops), the person being workshopped is not allowed to speak until everyone has said their piece. There's a good reason for this. There's nothing worse than someone who argues with every point that you make. (Yes, you've swapped hats now.) If people don't want criticism, they shouldn't put up their stories for workshopping. They shouldn't feel compelled to defend every word their written. After all, it's been put up because they want feedback on how to improve it, right? Not because they want their egos stroked. Well, that's the theory. The trouble is that some people do put up their stories so they can be told how brilliant they are.
I remember spending a lot of time workshopping a story that I thought needed a lot of work, and then the author very smugly telling me and the rest of the group that the story was already published. What a waste of my time. Not just disrespectful but rude as well. Did that mean we all didn't know what we were talking about? Not at all. I'm sure we've all read published stories we thought could have been better. Perhaps the writer (who was new to our group) had no trust in our abilities as workshoppers, but from that point forward we had no trust in her as a serious writer who was making good use of our freely given time.
A good workshopper will give specific, rather than vague comments. So, not: "This sucked big time, and I hated it..." but something more along the lines of: "I thought your setting and characterisation were great, but your POV was all over the place, and all that head-hopping made me dizzy..."
Good feedback will point you in the direction you need to go to get things working more effectively. Good feedback is constructive, not destructive -- with any negative comments justified and a balanced reporting of what works in the story as well. This is important, not just to help preserve the writer's faith in their story, but because someone else might have knocked the very thing that you loved, and the workshopper needs to know that you did love this aspect -- that it did work for some readers.
I'm currently going through reader comments on my novel, and trying to address a saggy middle. As I'm reading through the chapters, I keep seeing opportunities to expand, expand, expand. (Add more characterisation here, put a few more thoughts in there...) I'm working through, looking at scene purpose, commenting on how well I think the scene is working and how I can address any problems. I thought by now I'd be distant enough to be able to see these problems manifesting themselves, but I'm struggling. What should I do? Consider that I'm right and my reader is wrong? This could be the case -- it is always something you need to think about -- but sadly and happily for me, I don't think this is true. Why sadly and why happily? Sadly, because I know dealing with the problem is going to entail more work, and I'm going to have to keep wrestling with it, but happily because I also know the book will be stronger when I emerge out from under it. And really that's exactly why I asked my reader to read it.