I signed up for a Discover Miles Card as part of a zero percent balance transfer arbitrage plan. While the plan is working, I have found the reward (interest) is not worth the expense (time and effort). After I pay off the loan in a few months, I plan to stop using it.
One upside of the plan is the 2,000 bonus miles (provided I charge something each month) I earn. By charging something in the $20 range each month, I have accumulated 8,000 miles. After purchasing my Christmas plan tickets, I traded 5,000 miles for a $50 balance credit. Considering the amount of money "spent" on the Discover card, it has been a big winner.
Finally, I have to give them credit for good service and an easy to use website.