The risk, some analysts say, is that the rush of properties expected to hit the market in the next few years could give potential buyers plenty of choices among properties with similar amenities, such as designer furnishings, swimming pools, gyms and concierge reception areas, thereby putting some pressure on prices.

WSJ: London's Riverside Housing Boom

Although the rental agency might have a daytime reception desk and an emergency phone number, there's no houseboat concierge to get you tickets to the Concertgebouw.

FORBES: Playing the Float