I found this to be true in my day-to-day business:
Although the average square footage of a new house is still double what it was in 1960, in the last year it decreased slightly to 2,215 square feet from a high of 2,277 square feet in 2008, according to data from the Census Bureau. While the decrease doesn’t approach mid-20th century levels, it is the first drop in house size since the recession of the early 1980′s.

Source: REALTOR, February 2010