I have always been anal about spelling, ever since I was a child learning my brother's spelling words along with him. If I don't know how to spell a word, I get really frustrated. And if other people misspell something, I get really upset about it. It's just the way that I am.
Recently [I don't know exactly when], the oatmeal did a post about commonly misspelled words, and it was great. If you are someone who is always mixing up "your" and "you're", "their", "there", and "they're", or "its" and "it's", then this will go a long way to clearing things up for you.
And in advance, thank you for finally learning the rules of spelling and grammar.