I didn't see anything (with maybe the exception of FourBlades using inheritence and shadowing (and wanting Fx cop compliance)) that REALLY needed to be a writeonly property for a specific reason.

initializing a class by passing values to writeonly properties is the same thing as passing them to a constructor, and the wrox example could have just been a function. Not to say it is a bad example, I was just looking for an example where you HAD to use a writeonly property and using a sub/function or just a read/write property made no sense.