I said "always" and I mean "usually." It seems like I don't really notice them when I'm the author of the text. But to answer your question more seriously, yes, if I'm reading closely, I typically see errors. With that being said, I have to confess, my opinion of the author depends on whether they are perceived to be a native speaker or not. If they ARE a native speaker, and it's not just a handful of errors, then I form an opinion that they are ignorant/lazy and I don't really give the text as much respect. Is that fair? Maybe not, but that's the truth. If it is a non-native speaker and as long as I can follow the basic train of thought, then it's usually not nearly as irritating and I give them the benefit of the doubt in that regard. Does that make any sense?