Getty Mexico's Riviera Maya has been changed over the years from a drowsy backwater into a first-rate holiday location. And together with the tourist development, mobile professionals and digital wanderers have actually flooded to towns like Playa del Carmen and Tulum. "Tulum has actually cornered the market for being eco-chic," says McMahon.

It's as fashionable a destination as St. Barts, St. Tropez and the Greek island of Mykonos." Until now, a 1,000-square-foot oceanfront condo in…