I have a small reserve of patience, selectively used, for its/it's, as 'its' violates the usual possessive rule. Who's is a whole other issue and receives no allowances.

I got your card too! It was very cheering on my doormat as I walked in from the melting snow. (Very glad mine arrived safely, I'm 98% sure the post office site sold me completely the wrong postage and I did wonder if it was going to be travelling by slow boat or something.)