CNNMoney.com says the rental vacancy rate has dropped below 10 percent, and by 2012, may be as low as five percent, according to Peggy Alford of Rent.com.  The Commerce Department statistics report that rents have averaged an increase of below one percent a year for a decade.  Alford expects them to increase seven percent in each of the coming two years, and in the hottest markets, she says they will increase 31 percent by 2015.  People who lost their homes to foreclosures, and those who don’t want to take the risk after seeing their friends and family losing their homes, are in the rental market.  The balance will change as the foreclosed homes are eventually sold.