If you have difficulties actually listening to the message of a written text just because you're obsessively bothered by spelling-mistakes, then that actually says more about your very intelligence than the education of the writer.
You do know that the POINT of language (written as well as verbal) is making oneself understood to others. So if you can clearly understand what someone else is saying, regardless of spelling errors, then what is there to be bothered about?
I'll tell you what: the fact that some people are incredibly neurotic, most likely suffering from some kind of social disability that they lose the ability to focus on the subject matter and start nitpicking over trivial details like spelling errors. It's a sign of immaturity and a pretty textbook case of it:
"The word is supposed to be written like THIS, because THAT is what the teacher in school taught us, and you don't write like the teacher told us we should so im going to disregard the message I can clearly read and go ballistic instead!" *rage* <-- honestly, does that seem like a mature and adult reaction to you?
So to all you grammar nazi's or you who are just borderline grammar nazi's, take this to heart:
Yes, some people do not spell correctly, but if you can understand just fine what the person is trying to say, then it's actually something much more wrong with YOU when you react the way you do and even start to lose focus of what the person is trying to say in favor of being nitpicky. And in fact, that is a much more severe problem that you really should try to adress than being less than perfect at spelling or grammar.
So each time you feel the rage building up, try to think of what purpose language has. It's not a competition in who can remember how to spell most words correctly, it's a TOOL to make yourself understood.