I have a D300s which has 2 card slots, unfortunately IMO not both CF. I have it set to make a backup every time (records each image to both cards) This tends to slow it down, as SD cards are not as fast as CF, BUT - it gives me peace of mind that I have an immediate backup! (And I have needed it on more than one occasion) When holidaying, I always take a set of cards (usually 4 or 8Gb) for EACH day (I shoot RAW and 8Gb gives about 400 shots). This provides ma with even more backup! I have not had any reason to regret this procedure, but would have done if, as happened, one card went "bad" before retrieving the images off it. I have lots of cards - they are not that expensive, and lost images are just that - LOST!!