For me, it's like this...
When I read, some errors jump out at me. I can't help it. No one's writing is perfect, least of all mine, but when I see something, it jolts me. I just can't help but notice. (I wish that worked with my own writing, but when I try to edit something I've written, I tend to somehow skip over my own mistakes. It's very frustrating.)
I'm more forgiving of mistakes from writers whose native language isn't English, and I'm also more likely to speak up about an error if a story's overall quality is high. In a way, the fewer the mistakes, the more they stand out.
I also like to think of the boards version of a story as being in the later stages of editing. If it's here, then it's probably had a certain amount of polish -- enough to make it publically presentable -- but there's still room for tweaks, edits, and improvements before it hits the archive.
What I point out varies. If I really like something but there are a few minor things that jumped out at me (typos, grammar glitches, minor points of confusion, etc), then I'm perfectly willing to add them into a comments post as an (hopefully small) aside. If I know of an author's preferences, I'll certainly take that into account before doing so.
For myself, I like to have errors in my stories pointed out so I can fix them (or at least have that option, depending on whether or not I agree that it needs fixing). I don't mind having them pointed out in the comments thread, but privately (IRC, email, etc) works, too. So, I guess I tend to follow the Golden Rule there. The problem with the Golden Rule is that my preferences aren't always shared. The rule really should be something more along the lines of "Do unto others as, to the best of your knowledge and within the bounds of reason and morality, they would have you do unto them." If an author doesn't state a preference ("I need as much help as I can get!" "All comments welcome." "Be gentle." etc.), however, I have to either guess or assume that they'd want basically what I'd want in the same situation.
Paul
