I'm not a perfect grammarian or speller, but I do try my damnedest. What really frustrates me is the number of people that use an apostrophe to denote plurality: car's, book's, etc. Every single memo and sign at work is full of these, from upper management on down. I counted 19 spelling, grammar, and punctuation errors in the CEO's Christmas letter to the employees...and it was only a paragraph long!
Here's another one: it's vs. its. Aaarrrrrggggg!
It's (it is) your mother tongue! Learn it! All hail the Reich!