In my experience, the Sonos range can be up to 60 feet or more, depending on line of sight (for example, lying in my hammock outdoors and controlling a ZP80 in my living room). It's basically WiFi, so WiFi rules apply, although the Sonos system does become more robust the more ZonePlayers you add.
In my experience, poor signal does not affect sound quality, but it can create dropouts. In that case, a ZP80 can be used to bridge between units (not a cheap solution).
