I went to the Staples on 6th, in the 20s, and picked up a pack. I asked a woman who worked at Staples if I had the correct item. She told me that I did not. CDs were for backing up computer data. DVDs were just for videos, movies, and the like. I put the DVDs back, reasoning that she was the trained professional, as crash_mccormick might have put it, and that it really didn't make sense, after all, for me to be able to buy 25, or even 50, 4.7 gig DVDs that could do what I wanted for less than the price of a single 1 gig SD card.
But, I can. mneme pointed out that crash_mccormick uses DVDs for his back ups, and he confirmed this. So, I went to another Staples and bought a pack, and did my back up. Sure, I love the tiny SD cards, but they are quite expensive by comparison.