1. Interest rates that remain at historically low levels.
2. A government -- and an entire financial system -- that recognizes the need to keep the housing bubble inflated because it's basically become a Ponzi scheme that's likely to collapse after the last cohort of people can sell their homes with enough equity to retire.
You know, I really dislike how speculation has been seen as a legitimate means of making money. This isn’t supposed to be a form of a career and it’s only once or so a decade that there is every any kind of real estate boom. Half the over-development plaguing this country is due to endless speculation.