First, credit cards don't actually catch very readily or burn very well. I decommission my CCs by cutting them up and melting them. Mostly they melt but if I hold the lighter under one for a time it will, eventually, catch.
The ones I've tried burn with a weak guttering flame that is easily blown out. I suspect that the plastic has some sort of fire retardant that makes it hard to catch and easy to blow out. While burning it produces a lot of stringy black soot that makes a mess of everything it touches, and various noxious fumes. I the fumes are a serious health hazard if you are not burning a credit card in a very confined space but the fumes are clearly not pleasant or healthy.
For tinder I've turned to a solid tinder that is essentially yellow wax and chemical impregnated card stock. It rides well in the wallet, takes up little room, doesn't seem to deteriorate, and works quite well. I can't find, or remember the name, but I'm looking. Best Glide used to carry it as I remember it. Problem is that unlike gel and liquid tinder it doesn't deteriorate much so I bought my supply better than five years ago and haven't found it necessary to buy more. Alas ... good things that last a long time tend to disappear from the market.
Cool deal -- found it, same package and everything:
http://www.gearwild.com/servlet/the-103/BCB-Fire-Starting-Tinder/Detail IMHO this stuff is much better than trying to light your credit cards.
Second, there are conditions where you are better off finding shelter, to limit heat loss, than staying exposed and struggling to light a fire. Even the settlers, people who lit fires regularly and had their ducks in a row for lighting a fire in tough conditions, were sometimes stymied when it came to lighting a fire. Strong wind and driving rain might see them hunkering down instead of wasting energy, and remaining exposed, trying to light a fire.
Yes, I know ... folklore is that Daniel Boone could get a fire lit underwater in a snowstorm using toenail clippings and fiery looks. Over whiskey in a bar he would have probably seconded the claim.
Fire is not the be and end all of survival. It would be silly to overlook its benefits where possible but to focus on it at the expense of common sense self-protection is no virtue. Wiser often to hunker down, concentrate on reducing heat loss, let your metabolism warm you up, and wait for more favorable conditions.