We removed this shuttle from our Free Shuttle listings back in 2008, on account of the service being discontinued back then -- presumably either for lack of passengers, or as a cost-cutting exercise, given Station Casinos' ongoing financial woes, or both.
However, not long after we received your Question of the Day, we received an alert from a reader telling us that the shuttle was operating. Curious, we called Green Valley Ranch for the scoop, and here it is:
Ssshhh, this is a super-top-secret shuttle, so don't tell anyone! While Green Valley Ranch still operates a complimentary shuttle service for its guests to and from the airport, as do most major hotels in town, the service that used to also run you to/from Mandalay Bay on the Strip no longer exists -- officially; however, if you request a ride and there's a driver available, you'll probably get lucky.
Since these "secret shuttles" are not scheduled, we wouldn't advise relying on the service to get you back to GVR from MBay, unless you can make some specific arrangement with the driver, but it might be good for getting you a free ride to the Strip -- it's at least worth asking. Just don't tell anyone we told you, OK?