This is circulating via email (although the technique itself is quite old):
Thieves rig an ATM machine by placing a "trap" into the card slot. When an unsuspecting victim inserts his card, the machine appears to "eat" the card. The thief, acting as a good Samaritan, tries to help and in doing so, asks the victim for his PIN.
After the victim leaves, the thief simply pulls out the "eaten" card and now has possessions of both the card and the PIN.