Here is an interesting variation on social engineeing attacks, this one relying on our human nature to be attracted to free, interesting things… 
Dark Reading – Host security – Social Engineering, the USB Way – Security
… We gathered all the worthless vendor giveaway thumb drives collected over the years and imprinted them with our own special piece of software. I had one of my guys write a Trojan that, when run, would collect passwords, logins and machine-specific information from the user’s computer, and then email the findings back to us.