I spent last week on a Disney cruise vacation and found a usability lesson in a odd place: a coffee machine on board the ship.
I drink a lot of coffee. I have ever since my first winter while stationed in Anchorage, Alaska. Go figure. Coffee urns for large coffee service are well-known, common equipment to a lot of folks. They're simple and have had the same basic features since dinosaurs roamed: a large pot to hold the coffee, an optional heat source to keep the coffee warm, and a simple spigot to dispense the coffee.
The spigot's operation is simple: pull a lever, a valve opens, and a stream of coffee starts to flow. Release the lever, the valve closes, and the stream of coffee stops. It's a simple mechanical gadget that's worked well and is familiar to all regardless of which continent you're on, or what the local language is. You don't need a manual, you don't need a waiter to help.
The Disney Magic, the ship we were on, had some nice-looking coffee machines which appeared to be completely automatic: they looked like they were plumbed in to a water source and were complete with grinders and a brewing system. I never saw an attendant pour in any coffee from another source. The benefit to the Disney crew of this for an operation serving thousands of cups of coffee is pretty obvious: fire and forget. Load up your coffee beans or grounds, ensure the water and electricity is on, then simply monitor to make sure everything's fine.
The usability issue? The spigot. Some engineer thought it would be a great idea to make the valve system electronic instead of mechanical. Then they could set an amount to automatically dispense when someone triggered the spigot. 8 oz. cups are pretty standard, so the engineers could set the dispensed amount to 7.5 ounces and everyone would be happy.
Except 99% of the coffee-drinking populace is used to holding that spigot open with their hand instead of simply whacking it a bit to get the stream flowing.
The results I saw were really amusing, even when it happened to me: Want to simply warm up some coffee in your mug? Not such a good idea, because the dispenser pours out 8 oz., regardless. 4 oz of lukewarm coffee + 8 oz of hot equals 12 oz. total, which is 50% more than an 8 oz. mug will hold.
Worse yet, someone's initial instinct in such a situation is that the valve's stuck, so why not work the spigot handle a couple times? Whoops, another 8 oz. of coffee flowing out. Good thing the coffee machines had a plumbed drain, too, otherwise there'd been a tidal wave of coffee flowing over the floor.
Lesson Which Should Be Learned: Think carefully when you're trying to bend users' experience in a concept that's ingrained and accepted for a long time. We cherish thinking outside the box, and we love seeing UIs or system flows which give us a better experience than we've suffered through previously -- but sometimes some things are better left untouched.
(I also had a rental car which had a fuel gauge that was backwards. Every fuel gauge I've seen since starting to drive a long, long time ago has its Empty side on the left and its Full on the right. The Pontiac G6 we had showed Empty on the right and Full on the left. That's a dangerous change since someone's quick visual glance might lead them to believe they're at 7/8 of a Full tank when they're really 1/8 away from walking...)