The best part of it is the card is backed by CHASE. I use mine to pay for most of my bills and I write One Check to Chase every month. It was stolen last year, but dispute resolution caught it quick and I didnt lose a penny. They simply changed the number and the points carried over to the new card. During the summer push they double your reward points for gas/grocery purchases. I just came back from CR last week. I received 10% off items purchased at Boardwalk Disney Store. I had accumulated 700+ dollars in rewards(over the past few years), so needless to say I did not spend any money in the resort. I still have some left over for the next trip in 08!!
On what you charge. It shows up on your monthly statement as a total number of reward dollars available. It doesn't matter if you have a balance on the card.