The trend is to smaller houses, at least according to the US census. The average house size peaked in 2005 and 2007 at 2277 sq. ft. and by 2010 declined to 2169. Not much of a change, and it may reverse, but maybe the sign of a shift or at least a stabilization.
http://www.census.gov/const/C25Ann/s...medavgsqft.pdf