I got my PADI combo card in 2005, it's the last PADI card I obained. This thread was started in 2009, at which time I suggested a combo card might be the solution to some multiple card issues. The thread was resurrected this year, it appears PADI does not currently offer a combo card, that's a shame, it was a good idea.
I also have a card holder in my logbook. The only cards in it are MSD/nitrox, DPV (just in case needed for rental, never requested), and SDI Solo. I've never needed anything else for my activities. The one time I forgot a C card, the operator looked it up on the PADI webite quickly, without problem.
Dr Bill, I've always been tempted to show my LACUU C card when using a new operator but haven't ever tried it. Would still be fun