e index indicates that home prices in greater Boston peaked in September 2005 and have decreased 11.9 percent since. This peak was earlier than many other metros. For example, Las Vegas peaked in August 2006 and has declined 31.4 percent since its peak. The PMI Group predicts an 11.8 percent risk that the Boston single-family housing market will suffer a 20 percent decline from current prices. This compares favorably to Las Vegas and Naples, Fla. at 88.1 percent and 97.6 percent, respectively. After a dip in June related to a 90-day moratorium, foreclosures are up more than 22 percent over…