Funny story: We went on a road trip recently. Checked into a hotel, were given a magnetic stripe key card and a room number, hauled our bags upstairs, attempted to open the door to the room ... and discovered that it was already occupied. Another guest was already in the room, with the inside bar lock in place (so the door would only open two inches).

In a crazy coincidence, we spent the next night in a different hotel in a different city and the same thing happened again.

I was surprised by this. I had assumed that the system that tracks reservations, available rooms, etc, would somehow be connected to the system that reprograms the magnetic stripe keys. I thought it would be harder for the front desk to hand out a second set of keys without some kind of warning message ("Hey, you already checked someone into that room ... are you sure you want to give out 3 more keys to the SAME ROOM?"). Apparently I've overestimated the room key/reservation systems in place at most hotels (another commenter here mentioned using DOS for reservations?!).

So, does UPM solve this problem? :)