i'm only anal sometimes, honest
there is nothing - nothing! - that irks me more than seeing "it's" and "its" confused in a professional capacity. as this morning, when I picked up a bottle of Guernsey milk and was mortified to find that people who are paid large amounts to write marketable material on milk carton labels are, in fact, morons. I can't help it: this particular misdemeanour immediately lowers my opinion of the letter, sign, label or item by at least 73.8%, and this is not even to take into account its perpetrators, whom I would happily disembowel, with a fork.
for future reference:
its: possessive, e.g. "the girl and its dog". you cannot say "its a nice dog", because the "its" in that sentence possesses nothing.
it's: a contraction of "it is", whereby the extraneous "i" is replaced by an apostrophe. no, one may not say "the girl and it's dog", because expanding the sentence, it reads "the girl and it is dog", which MAKES NO SENSE ARGHASD;FLKFASD;LKJ
[edit] just realized that in my throes of mortified indignance I've ignored the gender pronoun possessive; i.e. it's actually "the girl and her dog", not "the girl and its dog". bah, whatever, the concept is there.