One great use of interfaces is for automated testing, the test class can implement the same interface specification as the code. A long time ago I also used st

One great use of interfaces is for automated testing, the test class can implement the same interface specification as the code. A long time ago I also used structuremap to automatically wire up default implementations of interfaces, which reduced the need to write boilerplate code enormously. It also helped separate concerns because separating out interfaces means I could concentrate on only the specification of the class.