Should make for nice floor heating/cooling... and some weird drafts through the floor! Such methods are close to impossible to use here - basement ceilings are inevitably either brick arch or cast concrete and all other ceilings are usually finished... crawl spaces are non-existant. Actually I like that - there are no spaces for critters, the beam ceilings are pretty much sealed up.
That method of ductwork is/was very common in the midwest until the 60's, when ready-ade ductwork became more available. My own home had about 50 feet (cold air return) in the main floor joist bays until I lifted it and had a new basement poured.
