File this under: "That's nice!"
Denver's high ranking comes courtesy of its growing arts scene and strong environmental initiatives (measured through LEED certifications). It comes behind San Francisco and Boston, placing first and second, respectively, which both scored high in arts and green-ness.
Sperling's also rates Denver 39th in its list of Best Block Party Places, 60th for Best Places to Live (2005) and fifth for both America's Least Manly Cities and America's Manliest Cities. Go figure.
(Meanwhile, the Springs ranks second for America's Best Cities for Dating.)