Private or Estate Backyard Railroads

I would like to start a discusion on private estate or "backyard" railroads and what roles they have in railroad preservationand the future of steam operation.
The concept of estate railroading is not new.
A good example of a 3' back yard recreational railroad is Ward Kimball's Grizzly Flats Railroad.
Many tourist operations got their start with privately owned collections. Nowdays it seems to me that these private railroads are quite diffrent than tourist lines. Back yard railroads exist for many different reasons, but generally speaking a ride on such a line is usually by an invitation from the owner. Estate railroads are also unique from railroad museums and generally are presented as such . Many times the equipment has been rebuilt or otherwise changed .
They vary in their level of authenticity of equipment with everything from real restored steamers to modern diesels to amusement parkish looking equipment. There are several operations in various stages of construction in the West.