If you carry a balance, you may pay a variable interest rate as high as 19%. And if you've been late with payments or used up too much of your credit limit, you may be hit with a penalty rate, which can run north of 30%.

Credit card penalty fees, meanwhile, have been on the rise for years. The average late fee in 2005, for example, was $34, up 162% from $13 in 1995, according to the Government Accountability Office. Over-the-limit fees, meanwhile, were $31, up 138% from $13 during the same period.

So no matter how many airline miles or cash back rebates a no-fee rewards card offers you, it won't be enough to compensate you for your very expensive credit card habit.