Even though I'm a grammar fiend, I make many, many, many, many, many, many mistakes (and forget to use the spell check too). I don't think I'm any expert with words. I do have a few pet peeves like misuse of lose and loose and affect and effect. I see those mistakes made all the time and by all sorts of people. BUT I make plenty myself, that's for sure.
I get po'd by the misuse of their and there. Even school officials get that wrong and that ticks me off even more.