2011-09-22 : Each opponent must sacrifice only one permanent for each trigger, even if the nonland permanent you controlled that went to the graveyard had multiple types. For example, if an artifact creature you control is put into a graveyard from the battlefield, each opponent sacrifices exactly one artifact or creature, and that permanent doesn’t need to be an artifact creature.

2011-09-22 : If Martyr’s Bond and other nonland permanents are put into the graveyard from the battlefield at the same time, Martyr’s Bond will trigger for itself and each of those other nonland permanents.