I have a little different procedure and ideas on using the cards and is only my opinion. Everyone has a different way and ideas. The cards are designed for data storage and letting data accumulate in them does not corrupt the data or do physical damage. More damage is done to these plastic cards with the constant plugging them in and out of the camera and in and out of a downloading device than just letting them sit in the camera and accumulate data until full. Data gets corrupted primarily from damaged or corroded contact points than anything else. It is always a good procedure is to inspect the contact points for damage and being corrosion free "before" putting them in the camera. Also never touch the contact points with your fingers. The only time I reformat a card is if for some reason I don't need the data already on it, or it's full, or I need the room. Unless I need the photos right then, I often will shoot several shots here and there over several days or even a week and then down them all at once. I use the cards for storage if I'm on a long trip where I will be taking 3k to 4k shots. I have 5 cards, two 8gb and three 4gb. If I'm on the road I download the card(s) each night but keep using the card until it's full and then go to the next card and put the full card in my bag. They act as a back up to the hard drive on my computer. When I get home I backup everything on separate hard drives and then reformat the cards. If I'm on the road more than a week I usually take a separate portable hard drive and back up the computer every couple of days but still keep the full cards until I get home. BTW, my pp program does not show photos that have already been downloaded from a card unless I want it to. So I only need to deal with the new ones.
I've been using this procedure for many years and it has worked well for me. Anthony's procedure also works very well and a lot of photographers do that way. The main point to remember is that these little plastic cards are the weak link in the taking, storing, and data transferring of photos. They are mass produced and even the best made are not that good. Because of being mass produced they can have internal defects that may not show up right a way. Caution is always the best procedure in the handling and transferring of data to and from them. And always backup and back up again.