10/4/2004: Each activation is considered a new damage effect. An activation can only be 1 point of damage.
10/4/2004: Note that "until end of turn" effects wear off after "at end of turn" triggered abilities, so an artifact that animates until end of turn can keep Pestilence on the battlefield.
10/4/2004: It will stay on the battlefield if there is a creature which is put into the graveyard at end of turn. This is because this ability will not trigger at all if there is at least one creature on the battlefield at that time. Remember that the current player's "at end of turn" effects resolve after the other player's because they are put on the stack first.
2/1/2007: This is the timeshifted version of Pestilence.