It is important to note that the Massachusetts data, while showing that 42% of the foreclosures were multifamily units, may be sui generis. A lot of housing stock in Massachusetts, particularly in urban areas, has 2 or 3 units and often has one owner-occupied unit. (In 1999, there were almost 16,000 3-unit buildings and over 18,000 2-units buildings in Boston per se and lots more in the suburbs.) "Triple-deckers" make up a good chunk of that: for a long time now, buying a triple-decker and renting out two units was one of the few ways to afford a mortgage in Boston for those of modest means. Alas, I cannot find data that separates owner-occupied multifamily from non-owner-occupied.
http://www.cityofboston.gov/dnd/pdfs/tripledecker18_webd.pdf
--tim francis-wright