"The term Don before a man's name, and Donna before a woman's name, may or may not indicate noble birth. For they were used not only for persons of noble rank, but for persons whose families were of noble origin, but reduced in circumstances as well. ``Downward nobility'' has never been a phenomenon foreign to Italy's nobility. Often, too, don and donna (translated as Lord and Lady) were simply titles of respect and deference used for a man or woman of some standing in the community, with wealth, education or position acquired, not inherited."-from Colletta-Italian Roots, p.106.
Don is also a title that was used for priests in the records, and today is used specifically for Diocesan Catholic priests. Over time, it also became a title used by the organized criminal societies-such as the Mafia-in southern Italy and Sicily. The feminine title Donna is rarely used nowadays. http://en.wikipedia.org/wiki/Don_%28honorific%29