Warning: Buying Investment Property May be Addictive

According to the National Association of Realtors, 35 percent "of all investment-home owners said they were planning to buy another home within two years. For those who currently own four or more investment units, 64 percent said they planned to buy another property within two years, and 17 percent said they planned to purchase five or more additional properties." Even though the air is leaking out of the housing bubble? I wonder. And what happens when interest rates hit 9 % or so?