data corruption - How often should memory cards be formatted?

Should memory cards in DSLRs be formatted every so often? If so, how often?

I hear that after emptying the card out (transferring images to a computer), that it's a good time to format it to help reduce the chance for error/corruption. Is this true?

I want to point out: Nikon D90 User's Guide by Ken Rockwell

From the site:

Always format your card after you put it in any camera, or if you've connected your camera to a computer.

Formatting your card(s) ensures any folder or file corruption acquired anywhere goes away.

You can shoot without doing this, however constant formatting is good practice and should eliminate ever having any card errors. Be sure you've downloaded and backed up all the files in two different physical locations before formatting.

Answer

I format my card every time I stick it in my camera and start a shoot.

I do this for a couple of reasons.

First, it means every time I start a shoot, I don't accidentally leave the previous shoot on it (and it also means I don't delete it until I start the next shoot, by which time those images are safely on various backup disks; gives me an emergency backup on the card until I'm sure I've got multiple copies elsewhere).

Second, I use multiple camera bodies, and I know people who've had corruption issues with cards formatted by the computer (which I never do) or by one body and used in another because the bodies interact with the card slightly differently. By formatting every time, I know the formatting is what the camera wants and is expecting.

Third, formatting at the start of the shoot will (or should!) catch a card that is starting to fail. At the least, it'll catch some early failure modes in the card -- and in two cases for me so far, it has. So if the card hits an error during format, I know to immediately retire it. I'd rather find out I have a card error at the START of the shoot that midway into it, or worse, when I'm trying to read the images out later.

Note: any time I get a card error, I retire that card. Cards are cheap. Dead cards that eat my only copy of an image is expensive. And formatting a card every time means that every time I shoot gives me a blank slate in a known state that hasn't reported an error. Which means many fewer potential problems later. And FWIW, I basically never run into corrupted cards, lost images or problems during a shoot or during a post-shoot import.

Even if it means the card will wear out sooner, I don't care. I want reliable cards, not ancient ones. I'll happily replace them rather than try to recover images from them....