A fellow sufferer in the apostrophe wars

A personal pet peeve of mine is the incorrect usage of “its” and “it’s.” It’s a simple distinction:
it’s = it is
its = a possessive form of “it”

One misplaced or missing apostrophe is all it takes to irritate me, but I’ve never claimed to be a patient person.

This sloppy misuse makes me crazy. Another thing that gets my goat is the confusion between there's and theirs.