Apostrophe Craziness

I was reading this article on random apostrophization that points out that some people use the apostrophe incorrectly.

It's kind of difficult sometimes to use that punctuation mark correctly. Once in a while, I have to stop and think if I'm supposed to use 'it's' or 'its'. While writing drafts at high speed, the apostrophe just sneaks into the text without permission sometimes.

And I do want my writing to be grammatically correct, at least when it's not necessary for me to bend the rules to better convey a meaning.

Incidentally, according to this article on the usage of apostrophe, I made a grammar error in Gloriously Messed-up - maybe even more than once. Apparently, 'Sis'' should be 'Sis's'.

i.e.

Big Sis' mouth dropped open.

   should be:

Big Sis's mouth dropped open.

   since Sis's is pronounced 'sissus'.

Ouchie.