Not only have 30-year fixed mortgage interest rates been at or below 4% since November 3rd, they also hit an all-time low this past week at 3.87%.
 
Buying a median priced home a year ago:
   Price:  $180,000
   Interest Rate:  4.81%
   Monthly Payment:  $884  (assuming 80% LTV)

Buying a median priced home now:
   Price:  $174,900
   Interest Rate:  3.87%
   Monthly Payment:  $781  (assuming 80% LTV)