An interview with me is currently featured at HotelsCheap.org. Excerpt:

What are the disadvantages of using [credit cards to earn miles]?

There are none if you are responsible.

If you are irresponsible with credit cards, don’t get them. There are two main ways to be irresponsible with credit cards.

1. You don’t pay the monthly balance in full. If you run a balance at 20 percent interest, any rewards will be quickly swamped. Just set your cards to be auto-paid from your checking account each month to avoid this.

2. You spend more with plastic than with paper. If you know you spend less with cash, don’t get credit cards because any rewards will be quickly swamped.

Check out the full thing here.