I can be really nitpicky on that as well, not perhaps the spelling (though if there's a lot of mistakes it'll bother me, as would bad grammar) but how certain sentences are worded etc. Though, to be honest, the way a story looks bothers me more than how it might, at times, be worded. That's actually why I like ff.net, because the screen is clear and the font easy to read (it's also easy to make the words larger and you have the choices on the full view, the half view and the 3/4 view). So if a story is somewhat badly written, I am more likely to read it than a story with the same "faults" (as I would see them) that was posted with a lot of unnecessarily long paragraphs, tiny text that couldn't be changed etc.

But, more than anything, the plot is most important to me when deciding on if I want to continue to read a story or not despite whatever flaws I might find with it.