After recently getting lost for the umpteenth time, I decided to join the 20th century and purchase a GPS navigation device. Shortly after making this decision, Groupon delivered a great deal to my email inbox: a factory refurbished Garmin GPS ($240 list price) for $69. A day or so later, ready to purchase, I went to the Groupon web site only to discover that over 25,000 GPS units had been sold and the deal was no longer available. Wow, I thought: That’s a lot of GPSs to move in a short period.