Apparently this has been going down for a few years now and the folks who are doing it are pretty good. Thailand, Cambodia and Vietnam seem to be where it originated from and there's rumors that Filipino organized crime has a hand in it. Anyone that travels to that part of the world should be aware of it (and it's probably not long before it makes its way to other areas such as South America), so just keep your head up.
Frankly for me it brought back memories of my own near-scam situation with Three-Card Monte during a trip to New York City in the early 90s...but this is much more elaborate and designed to fleece the victim of thousands. As usual, the victim's greed is this scam's greatest strength:
http://www.lonelyplanet.com/thorntre...readID=2197491
Don't know if this is credible, but one apparent travel blogger's juicy account of his run in with Poker 21:
http://johnnyvagabond.com/featured/poker-scam-saigon/