Developers Try to Limit Speculative 'Flipping'
Nancy Levy sent this Washington Post article on a subject I've been hearing about from several sources. Developers are trying to limit the number of speculator-buyers. I've heard (not in this article) of including covenants that commit the purchaser to not selling until at least a year has passed:

For the past few years, it has been a way to make easy money: Sign a contract to buy a property when it is still nothing more than a few squiggles on a builder's plans. Then, when there are four walls and a floor, or even before, flip it to another buyer, making a profit without ever moving in or even being a landlord. With prices and demand climbing around the Washington region, such investors could make hundreds of thousands of dollars during the two years or so that it takes to build a condominium complex, townhouse or housing development, with just a small down payment at risk...