In March of 2009 vacant stores in downtown Berkeley, CA started showcasing art in order to make empty shops more attractive and allow artists to use available space. The Berkeley Office of Economic Development and the Downtown Berkeley Association were involved in the initiative.
Here is an informative article (including a slideshow) from the Daily Californian.

The San Francisco Arts Commission Art in Storefronts project received a big kick-off in October and appears to be going strong. In contrast to Berkeley, the storefronts in downtown San Francisco integrate the entire site as part of the artwork. Chloe Veltman writing in The New York Times shares her thoughts here including an interesting take on the relationship between art and commerce.

Artists in the U.K. also used vacancies to display their work earlier this year – click here for the article.

All of this points to the important role of art in helping cities survive economic downturns but also begs the question; why do we have to wait for a recession to see so much art?