The great Mr. InkUnderNails started a thread about this a few weeks ago, do a search.

Ironically, my CP holder (son) just got an elaborate CP card complete with fancy envelope and plush card holder a few months after I first designated him as such. First time I've ever seen this card, never asked for.

I was stuck in the Irene mess doing MCO-ISP and couldn't get back for a week afterwards (eventually drove 1300 miles). I wondered if we had to split up whether they would accommodate us on different flights and still honor the CP. Never asked though as we were really a party of 6.