It definitely IS a fad, but there are a few differences between them and an RV. Tiny houses are more like FEMA trailers in that they have no holding tanks or fresh water tank and need to be hooked up to water & sewer. They are built much better (usually) and heavier than an RV though, and are meant to be lived in permanently. (The RV industry gets by with a lot of **** as they don't intentionally build units to be lived in permanently.) Other than that, the comments about storage space & cost are right on.