Map them as private roads when:
- The driveway is long -- perhaps double what is a typical distance from the road for a house inside city limits? Not sure of actual length, but that sounds about right to me.
- The house location is very close to another road without access to that road so that correct directions can be provided. This may go away once we are using entirely internal address mapping using the stop points.
- The driveway supports more than one house.
- The driveway is named with an official street sign (not a custom sign).
In addition to residential driveways, all actual roads should be mapped regardless of whether or not they are private. If it's a gated community or even just one that has a posted "private road" street sign, it should be mapped. It doesn't matter if it's a private facility, government facility, or housing subdivision. If it is a road (as opposed to just a driveway), map it.
We'll leave parking lot roads for a separate discussion if needed, though I have to say that I *support* mapping drive-thrus and any parking lot with more than a couple GPS tracks in it, even if it's just a single parking lot road in and nothing else. If there aren't any GPS tracks, then it doesn't need anything in it until/unless we decide to mark all commercial lots somewhere down the road. Traffic problems are an obvious concern and driving in the middle of a white space just looks really amateur. We already have that problem with Street types where you can't see the road you're on.