Many South Florida home buyers in the boom years between 2005 and 2007 now owe banks more money than their homes are worth, according to real estate Web site Zillow. A recent survey shows that 76.2 percent of homes bought in 2006 in Palm Beach, Broward and Miami-Dade counties are now worth less than the balance on their mortgages. Zillow spokeswoman Amy Bohutinsky said the situation could lead to more foreclosures. Of South Florida homes sold in the second quarter, 29.2 percent fetched less than their seller paid. In the Treasure Coast, 36.2 percent of homes sold in April, May and June created a loss for the seller.