I have come across a great explanation of what it will take, recently published in a real estate industry newsletter called Keeping Current Matters
In order for the real estate market to come back in a powerful way, five conditions must be met. Those are:
1. Increased buyer confidence in their jobs and income levels
2. Ease of housing price declines to market stability
3. Affordable housing in relation to household income
4. Access to mortgage financing with low interest rates
5. Ability to sell one's own home in order to move into a new one
Two of these conditions are in effect right now-- affordable housing in relation to household income and access to mortgage financing with low interest rates. The other three have not yet been accomplished. The market will turn around when all five forces combined can drive the rebound.