Yes, I do use my card for emergencies. Only when I absolutely need it though, because it's a lot to pay off, and I generally can not always added it.
I actually don't have an emergency credit card, but I think that this is a great idea. I will most definitely look into a card with no annual fee that I can keep just for emergencies. I, like others on this post, live off of my credit cards (but pay them off every month so I do not have a balance hanging over my head). I am trying to start up an emergency fund, but that, as many of you know, takes a lot of time - you need to have extra money to store away in order to really get an emergency fund up and running. I think once I have a pretty nice emergency fund - even if it's just a few hundred dollars - I'll look into credit cards. That way, I can use the credit card during emergencies, but know in the back of my mind that I can pay off the balance with the emergency fund I have growing.
The use of a credit card is directly connected to your credit score, the report card for borrowers. The responsible way you handle your credit card is recorded in your credit history for lenders to review. Your high score in that credit report shows how creditworthy you are deemed by other lenders and that you pay your bills on time and spend conservatively. Conversely, irresponsible use of a credit card will produce low credit scores which can result in either being denied for future credit or paying much higher interest rates.
I do keep one for emergencies. I've had to use it in the past, too, and was thankful that it was available. For example, my alternator went out while I was out of town and it was my only way to get anywhere. I needed several hundred dollars by morning and I was able to use the card.