As of the end of March, 2008, there were 129.4 million "housing units" in the United States. According to a report released by the Census Bureau on Monday, 18.6 million of those homes are unoccupied -- an increase of one million over the first quarter of 2007.

18.6 million unoccupied homes sounds like an awful lot. No wonder there was a housing bust! But that number is a little misleading. 4.7 million are for "seasonal use" only, the Census tells us -- unoccupied vacation homes, in other words. 4.1 million are for rent, 2.3 million are for sale, and the remaining 7.5 million "were vacant for a variety of other reasons."

The key figure is 2.3 million -- the total number of homes that are empty and for sale. That adds up to a vacancy rate of 2.9 percent, which is the highest, reports Bloomberg, "since the bureau started keeping count in 1956." 2.2 million homes were vacant and for sale one year ago.

According to the Department of Housing and Urban Development's Second Annual Homeless Assessment Report to Congress, released in March 2008, "the total number of homeless persons reported on a single night in January 2006 was 759,101."

Assuming that number bears some reasonable relation to reality, that would mean there are 24 unoccupied homes for every homeless person in the United States.