The US Postal Service has managed to develop systems that would never receive approval if they were to be implemented in a waterfall manner.
Through waterfall, by the time requirements were gathered, the cost was way too high to get the project started. Of course, the problem is people don’t know what they really want, so they ask for everything they can think of.
Using an agile approach, they start the project, and develop the minimum they can. Then, based on feedback and usage patterns, they develop additional functionality. A great use of Agile, and one more case where it’s allowed a company to build a system that does a better job than the old process, and saves them money.