Real estate investors are helping to keep the national housing market moving in a positive direction.  According to the National Association of Realtors, sales of previously occupied homes rose in March to an annual rate of 5.1 million, a 3.7% increase from February.  But it's still shy of the 6 million homes a year that economists say will indicate a healthy market. Foreclosures and short sales made up 40% of the market. Investors are certainly leveraging market conditions to realize a significant ROI in future years.