Many banks are now allowing you to take cash out at an ATM even if you don't have enough in your account. This may sound generous of them until you realize they are doing this to make big overdraft fees from you.
Of course, it would be easy for the bank to program the ATM to alert you if you try to take more than you have in the account, so the intention is clear. They want those fees, even if getting them comes from a mistake on your part. To avoid this, check your balance before you make a withdrawal (so far there is no fee for this).
This article comes from Steve Gillman's Secret Information Newsletter. I highly recommend signing up for it at: www.TheSecretInformationSite.com