Home prices across the nation rose for the second month in a row, according to the S&P/Case Shiller Index, a closely watched indicator for the housing market. The average price of single-family, residential homes in the United States increased by 2.2% in May 2012 compared with the previous month for both the 10- and 20-city composites. On an annual basis, both composites and 17 of the 20 MSAs saw increases in May compared with April 2011. The exceptions were Boston, Charlotte and Detroit.