There’s a great article on the history of moving sidewalks in New Scientist Magazine (thanks to Planetizen).
I think moving sidewalks, or some other type of continuous transport system, would be a great feeder system for regional (US: commuter) rail systems. This would enable the stations to be located a bit further apart in urban areas than in a ‘normal’ subway system – reducing operating costs and making service on the regional system more attractive (fewer stations = faster). Regional rail systems build with this model could follow the Zürich S-Bahn model, many lines operating through a central section that branch to different suburbs when they leave the center.
An interesting compliment to the moving sidewalk/continuous transport system would be combining it with attractive urban design, in other words give the people traveling on the system something interesting to look at while traveling. I recently had the idea of creating such a system in Abu Dhabi as part of their new Metro project. In this case the continuous system could travel through a traditional Arab linear market street setting. The market street would be protected from the weather in traditional ways, thus reducing energy use. The project would combine ‘new’ urban development with the transport system. More on this idea later.