Thanks to TMBG, who I always rely on for relevant financial security info (Irony Disclaimer: TMBG is the musical duo "They Might Be Giants"). They posted a link on Facebook to the Krebsonsecurity blog that has a very interesting post about the nice folks who steal our PIN numbers at ATMs. The videos are amusing, but the point of the article is simple - COVER YOUR HAND AS YOU PUNCH IN YOUR PIN NUMBER.
PIN numbers and data encoded on an ATM card are stolen by installing a combination of "skimmer" devices that read the card and a miniature camera to capture the PIN number as it is typed in. This could be at a bank or a gas station or wherever. Don't think that you would be able to spot a skimmer device, either. Those things are precision built to verify tight specifications. Some of them are so small that they slide right into the slot where the card goes.