I don't mind how people spell, as long as they show they're making some kind of effort. If someone writes in his native language in a bad way, and I can see that it's a consistent problem, then I tend to start losing respect for them.
If you're English and you've lived here for 16 years, surrounded by and using the same language then there really is no excuse. Well, unless your parents locked you up and didn't let you go to school.
Freefaller, I agree that people can expand their vocabulary by reading decent books; it's a very healthy way of improving language.
I have been learning language and studying linguistics for about two years now, and French is, by far, the most difficult language I've studied. I'm studying Chinese at the moment and I even find that much easier than French.
What I'd be interested in knowing is, do they suffer the same problem in France, regarding spelling errors and/or bad grammar?