I had one card fail (that I posted about here a couple months ago). I had dropped the card on the garage floor (the card is light - and relatively ductile - so there aren't a lot of Gs created by dropping it on concrete). As a result I lost about 6 images from the card. I can't swear that it was caused by the drop, but I did see the images in the monitor before the card was removed from the camera.
POed me because I had a perfect image that the wife wanted of her dream house - perfectly formatted and lighted. It could be a full year before that opportunity presents itself again!