Well the easy answer is only the people who have to sell an existing home first!!!
Never, never, never has there been a more opportune time for buyers than today. The lowest interest rates in 30 years PLUS the lowest price homes in 20 years! Come on people! Don't make a $30,000 mistake just b/c you want to wait a year! It's the biggest and best investment in your life! Why not start it out right?
OUCH!!! I just fell of my soapbox..........