Social networking sites and websites hosting forums grew their market share by nearly 62 percent during the year ending in May -- the largest gain among any real estate-related category, according to a new quarterly report from online metrics firm Hitwise.Visits to websites in the real estate category during May were down 24.3 percent from a year ago -- the 12th consecutive month of year-over-year traffic declines dating to June 2009, the report said. Hitwise's quarterly US Online Media Round-up showed rental sites featuring homes and apartments grew their market share by 24.9 percent during the same period. In a webinar last month discussing findings through April (see charts above), Hitwise's director of research theorized that the rental market for houses and apartments is benefiting fr...